Gear can only help you so much. Without some experience in the outdoors, your $600 puffer jacket and titanium Swiss Army knife won't be enough to save you.
That said, having the right gear can greatly enhance your trail experience. Below are my recommendations for your camping, hiking, clothing, toiletries and other supplies.
the essential gear
Pack (60-75 liters). Your pack can make you or break you. Fit is very important when you're lugging 50 pounds around a trail for 5 days. If at all possible, bring your own pack with you to Patagonia rather than renting one in Puerto Natales. You'll be just fine if you have to rent - but it's just a bit of a gamble what size and quality will be available. I splurged on my Osprey Aura 65 AG Pack - but it was worth it because it has made backpacking so enjoyable and will last me for many, many trips. The "anti-gravity suspension design" makes carrying 50 lbs feel like 10.
Tent. If you don't want to carry a tent with you when you're traveling to and around South America, renting a tent in Puerto Natales makes good sense. You can rent a three-season backpacking tent for just a few dollars a day at any rental shoppe in town. Ask for the lightest tent they have and always be sure there are enough tent stakes to set up the rain and wind fly.
The warmest sleeping bag you are willing to carry. You may be tougher than me, but boy was I cold every night! Women tend to run about 12 degrees (f) colder than men (and I tend to run about 12 degrees under that). Additional warmth comes at a cost, however, in terms of both price and added weight. I ended up renting a warmer sleeping bag that was almost a pound heavier than the lightweight three-season sleeping bag - but for me it was worth it.
Sleeping pad. Your back will thank you. You can rent a decent sleeping pad from one of the rental stores in town or bring your own.
Luci Light and these neat yellow twisty cords. I love our Luci Light. Prior to going to Patagonia, I bought these cool yellow multi-function ties from REI and used them to tie our Luci Light on the back of our packs so she could soak up the sun and recharge all day long. Those twisty ties were also used at camp at night to hang the Luci Light in our tent or secure clothing that needed to dry to trees. They are one of my favorite little camping gear hacks.
Camping stove or JetBoil. We brought our JetBoil stove from home, but many rental shops in Puerto Natales rent camping stoves and plates/utensils to go with it. We used the JetBoil to prepare breakfast, coffee, and dinner each day (see Food for more information).
Camping stove fuel and lighter. Buy both in Puerto Natales. The TSA will thank you. We brought 2 fuel cans on the trail for us both to use and we only used one.
Utensils and bowls. We brought a single plastic mug for our morning coffee and we just ate our dinner out of the backpacking food pouches. We each brought a titanium fork/spork.
hiking gear
Dry bags. Dry bags are a great way to keep important items like your passport, phone and camera dry, organized, and accessible in your larger bag. You can get dry bags of various sizes at any outdoors retail store. I brought two bags: one smaller dry bag carried my phone, keys, headlamp, extra batteries and wallet contents. The medium-size bag was reserved for my camera if it rained.
Compacter trash bags. Bring 5-6 thick trash bags from home. Wrap all your gear in the trash bags, then place it in your pack. Do not bother with pack covers - the wind will whip those right off!
Zip loc bags. We brought 5-6 durable zipper-seal gallon-size bags from home. We used these to store food or to transport waste if we had to blow our noses or whatever on the trail.
Camera. Don't show up to the most beautiful place in the world without a camera. I brought: Canon 6D, 17-40mm wide angle lens, 50mm lens, and a telephoto lens. Plus, a gradient and circular polarizer filter. I did not bring a tripod (I'm not a masochist). If I could do it again, I would have brought 2 lenses instead of 3 (a wide-angle and telephoto, or Canon's 24-105mm).
Trekking Poles. Jeff and I used to think trekking poles were dorky. I'm now a convert. Trekking poles help alleviate pressure off your knees, engage your arms, and keep you upright when the powerful wind tries to blow you over. If you don't want to fly down with your own, you can rent a pair for dollars a day in Puerto Natales.
Water bottle. A simple 20 ounce water bottle will do. You will cross a fresh water stream just about every hour on the trail.
Headlamp with change of batteries. You'll need it for getting around camp at night and for your pre-dawn ascent up to the Torres on the final morning. I like my Black Diamond rechargeable headlamp (be sure to charge it before leaving town).
Cash. You will need to bring enough cash in Chilean pesos (CLP) to cover the entrance fee to the park (18000 CLP), the catamaran fee (8000 CLP), the minibus (2500 CLP) and any incidentals. We brought extra cash to buy a celebratory beer (which cost 4000 CLP each but was so worth it). There is also a food stand at the end of the hike and so bringing some cash for a post-hike treat is highly recommended. Campsites at the refugios typically take most international credit cards or cash.
clothing
Keep in mind that between your sleeping bag, food and other essentials, you don't have a lot of room left in your pack. I ended up taking only 2 outfits (with the exception of socks - I packed 4 pairs) and re-wearing everything two or three times. If you are wearing the "right" kind of backpacking material, they will wick away moisture and you won't smell too bad by the last day of the trail. Merino wool is particularly good for re-wearing without offending your hiking company.
Boots. Bring a good pair of hiking boots. I would recommend a sturdy waterproof pair - you will cross streams and parts of the trail are very muddy (I love my Lowa Renegades). Most importantly, your boots should be broken in and tested before you go. If you haven't hiked at least 20 miles in them already, get going on that. Don't ruin a good trip with blisters.
Wool. Don't bring weak-ass cotton with you - you'll sweat, you'll freeze, you'll be miserable. Anything with cotton has no business in Patagonia. Wool or wool blends are the way to go for your socks, baselayers, and warm layers.
Fleece and down jacket. The best thing I can recommend is bringing a fleece and a down/puffer jacket. I brought a teal 650 down fill Marmot jacket. It was enough but when I go back I will bring my Patagonia Down Sweater Jacket with 800 fill. It packs down just as much and keeps me toasty at camp at night.
Rain jacket. All travelers to Patagonia should have a good rain jacket. While we didn't experience rain on the trail, it was nice to know at any moment I could throw one over my down jacket and stay dry.
Hiking pants. As a lady, I wore stretch/exercise pants (example). I brought two pairs. I wore them during the day and slept in them at night. They were comfortable and warm enough. Jeff, as a dude, wore waterproof hiking pants (example). He brought two pairs and also slept in them at night (with a thin merino wool baselayer underneath). At the time of year we went (late March), I didn't see any hikers in shorts.
Shirts. I hiked every day in a longsleeve synthetic or merino wool blend shirts. These shirts were warming but most importantly breathable. During the evenings, I threw on a fleece and on colder evenings my down jacket. I never felt too warm wearing long-sleeves.
Wool socks. I packed 4 pairs. Two pairs were thicker wool socks for colder days or sleeping in at night. The other two were super moisture-wicking blister-preventing socks that I picked up at REI.
Gloves and a hat. It gets cold at night. I brought a wool hat and some simple gloves. I wore both most nights. I recommend a pair of gloves that you can wear and still assemble/disassemble your tent, as in the evenings and mornings you'll want to wear them while at camp.
Pro-tip: Don't own a lot of hiking wear? You needn't spend a fortune! I found most of my base layers at Goodwill and other thrift stores. You can also rent warmer gear in Puerto Natales (here's a sample price list).
TOILETRIES
If you hike the way we did, you will need a few toiletries and can forgo most others. I didn't pack shampoo, conditioner or makeup, for example. Everyone on the trail had the same healthy glow of not showering for a few days, so feel free to be lax on your vanity.
Sunscreen. Because sun.
Sunglasses. Because sun.
Chapstick with SPF 15+. Because sun. And wind.
Hair ties, headbands or hat: Have I mentioned it gets windy? If you have long tresses, you'll want to pull your hair back a lot.
Comb. By day 2, I had my hair up for the rest of the hike. Every now and again I would try to comb my wind-swept bangs back into place. It was mostly a lost cause but you may have more success.
Dr. Bronner's Soap. This "18-in-1" hemp soap is pretty handy for backpacking. It works as hand wash, toothpaste, dish soap, shampoo, and laundry detergent (I have no idea what the other 13 functions are but I'm sure it's good for it). I like the travel-size liquid peppermint soap.
Toothbrush and toothpaste. Because you're civilized. Dr. Bronner's soap can double as toothpaste if you want to keep things simple.
Bug spray. We didn't encounter any bugs on the trail, but we were there in the colder months. Just to be safe, bring a small amount of bug spray with you!
Moleskin. Even though you totally broke in your hiking boots before coming to Patagonia (right?!), you never know when you may start to develop a rub.
Contacts. If you wear contacts, bring a spare few lenses and some travel-size solution. Can you imagine anything sadder than losing your only contact on Day 3 and not being able to see the views on the trail?
For the bathrooms: You really should make every effort not to have to go to the bathroom outside of the designated camp areas. In case you just can't help it, I recommend bringing a ziplock bag with the babywipes, hand sanitizer and a separate waste ziplock bag.
GEAR YOU do not need
Water filtration system. Leave it at home. The water in the park is pristine and you will come across a flowing river/creek every 20-30 minutes on the trail.
Big water bag. For the same reason as above, I'd save the weight and just take a bottle for refilling. You'll cross streams often enough and all the campsites have running clear water.
Backpack cover. Great idea in theory to protect your items from the rain, but the Patagonian winds will rip that right off your pack. Instead, pack your items in trash bags to place inside your bag. The outside of your pack may get a little wet but the insides will stay dry.
Book. Jeff and I both hauled around a book each on the trail and never read a single page in the five days we were on the trail. When we got into camp in the early evening, between setting up your tent, preparing dinner, chatting with the other hikers, and getting ready for bed, there was not a whole lot of time to read. Not to mention after a day of backpacking we were wiped and fell asleep within 20 seconds of hitting our pillows. We never even had a chance to open our books and yet I hauled George R.R. Martin's fat Song of Swords for five days. If you know for sure you're going to read, then go ahead and bring one along. Otherwise, trust there are other ways to entertain yourself at camp every night and save the space and weight.