Don’t forget the small necessities: Most places you will go to won’t have toilet paper or sinks so you NEED tissues and hand sanitizer. The altitude affects everyone differently—for me it wasn’t too bad— but you can get headaches and stomach aches easily. My mom took a medication to help her with the altitude sickness. I took it one day but didn't really notice a difference. All I got were mild headaches pretty frequently so I would recommend just taking an Ibuprofen or Advil unless you know that you are bad with altitude. I also think a portable charger would be a good idea to bring because the sites are beautiful and you will want to be well charged to take all the pictures. Although the outlets are the same as the US ones, it is good to always have a portable one handy incase you can’t find an outlet
Buy some good hiking shoes: I really didn’t want to invest in ugly hiking shoes that I wouldn’t ever wear again, but they honestly saved me. With all of the ruins you will visit and especially for the Inca Trail, they are a necessity. Reasons: 1. They have great support and will help your feet be a little bit less dead. 2. They are waterproof and no matter how many puddles you step into or how hard it rains, you stay dry and warm. 3. They have a lot better grip than regular sneakers and make sure you don’t slip. I recommend wearing thick REI socks with them and make sure you bring those socks when you try the shoes on to buy them. Also, if you aren’t used to the low boot style shoe, it will be very uncomfortable. I got the regular low top shoes and they were really comfy, I got them 2 days before my trip and didn’t even need to break them in. They are brand Ahnu (click to see which ones), and my mom got the North Face ones and also really liked them. I didn’t want to get these shoes because they are pretty ugly and I didn’t want them to ruin my pictures and outfits, but honestly it doesn't matter at all. Everyone is wearing uglier shoes and jackets than you are, and even at the restaurants at night in places like Aguas Calientes and Urubamba, everyone is dressed like a hiker.
Dress in layers: This once again will be more helpful if you are also going in December. Bringing one big warm raincoat will not be helpful for this time of year. When you leave in the morning you will be pretty cold, but once you start hiking you get so hot with your coat. What I would recommend is wearing long pants, sportswear/dri-fit type of shirt (tank, t-shirt, or long sleeve works), one puffy jacket that warms you up but isn’t excessively hot, and a thin rain coat whose only job is to protect from rain. I liked this because I would usually take off my jacket and stay with just my shirt, but when it would start to rain I would put on my thin rain coat so I wouldn’t get wet but I also wouldn’t be too hot.
Ask for waiters at the hotel to fill up your water bottle, no matter how awkward it may be: If you want water, you have to buy it. The only time you get free water is in the complimentary breakfast, but there isn’t much of it and they try to hide it. Even though it might take a while and they will be a bit hesitant, always bring water bottles and ask people at the hotel to fill them up for you before you leave for the day. Drinking lots of water helps with the altitude soit is important to always have a few bottles handy.
If going to the 2 day Inca Trail or even Machu Picchu, bring a backpack: My brother and I both brought our backpacks just as our carry on bags, but ended up using them more than we thought we would. I recommend bringing a good sturdy backpack for each person on the trip so that it lightens the load a bit. You need to bring all of your water and food with you on the Inca Trail, plus your clothes for that upcoming night so you need to make sure you have space for everything but still pack light. I like to pack using packing cubes (not any specific brand but you can find them easily in many places) because these help conserve space and I would highly recommend them for this. All four of us folded our clothes into two of the small ones and it saved us a lot of hassle. Not only do the packing cubes save space by compressing all of the clothes, it also makes backpacking so much easier because if you are looking for a certain item in a bag, you don't have to spend time looking through a ton of clothes. Anyway, we sent our real suitcases with our driver from Urubamba to Cusco, and took the Peru Rail to the 104 km checkpoint of the Inca Trail. With only our backpacks, we went all the way to Machu Picchu and then down to Aquas Calientes where we stayed the night. For this reason, you need to have a backpack. Everything we carried on the hike was all we were going to have for the next two days. We realized this very last minute so we bought a cheap backpack in one of the stores and it broke from the weight! I used this backpack and although it is my school backpack it was super good for hiking because it had two straps and nice padding which didn't hurt my back.