Water Containers: I recommend you carry 2 quarts of water with you - 1 of them easily accessible, so you can get at your water by yourself, without having to take off your pack. I have a 2 quart hydration system in my pack and carry 1, 1 pint Nalgene bottle in the side pockets of my pack that I can reach with the pack on. There are also holsters that fit onto the waist strap of your pack to hold things. I am asking you to bring 2 containers so that you can be purifying one bottle with tablets while still being able to drink from the other. Liter Gatorade bottles make good water bottles - they are strong and lighter than a Nalgene bottle.
Eating Utensils: Cup, spoon (and optional fork), and bowl. The bowl needs to be large enough to also serve as your plate, and I use a spork - a spoon with little tines that allow it to be a fork/spoon in one. The heavy-duty plastic utensils or metal ones sold at outdoors shops work great. (Don't bring plastic disposable utensils- they will break). You will not need a knife for meals, but if you want to bring a small pocket knife, it occasionally comes in handy (think marsh mellow sticks). Put your name on your dishes and utensils. Your goal here is to have a way to drink a hot beverage, eat soup, and have a plate for the main course. Some people use a mug for drinks and for soup and bring a plate and then you don't need the bowl. The drawback to this system is that you can't have hot coffee and hot cereal at the same time. It's your personal preference.
Flashlight/Headlight: All you need is one or the other and an extra set of batteries. A headlamp gives nice, hands free use, but if you don't already have the headlamp, a small, light weight flashlight is fine.
Rain cover for pack: You can buy a rain cover or make one using a large garbage bag, cutting slits for shoulder/hip straps and reinforcing the slits with duct tape. A rain cover is also useful to cover your pack at night to keep dew off of it if your tent is too small to have the pack inside with you. I will probably line the inside of my pack with a plastic garbage bag and use a poncho for rain protection for both me and my pack if it rains while we are hiking. I generally stash my pack inside my tent, and if it's cold I sometimes put my feet inside of it.
Bug Repellent: We don't know what to expect. To carry a little repellent is good insurance.
Personal Meds, 1st Aid Kit: Bring with you any medications you regularly take; both over the counter and prescription, and some very basic first aid supplies. You should be prepared to treat your own blisters and minor aches and pains. I will be carrying a group first aid kit for emergency situations. Women should carry menstrual supplies, even if you don't anticipate needing them. The exercise can alter your regular schedule. We do not carry or administer OTC medications such as Advil and aspirin - bring your own. Besides sore muscles, blisters are the most common problem that we see on the trail. My personal system is to cover my vulnerable areas (in my case it's my heels and the side of my little toes) with a piece of white, athletic tape before we ever start hiking. Athletic tape is available by the roll in the drug store, and I would be happy to show you how to do this. One taping will probably last the 3 days that we are out, so you would not need much. Other people swear by moleskin, but I find that it doesn't always stay put on your foot.
Required clothing item: Rain Gear. It's a fact of backpacking life that if it rains hard enough, you will probably get wet. A rain jacket and pants can be expensive, but they can double as warm clothing if the rain is light and they stay dry enough to layer with other clothing in camp. A poncho gets caught in the wind, and you get wet, but during the summer, it is generally my first choice as it allows the air to circulate so I don't overheat. This is another one of those areas of backpacking where there is no "right" answer. During my first year of backpacking, my rain gear was a yellow Mickey Mouse poncho.
Long Pants: Don't bring denim long pants. They weigh too much and take too long to dry if they get wet. I have synthetic pants with lots of pockets that the legs zipper on and off. Those are my shorts/long pants combo. I also take long underwear and rain pants.
Long Sleeve Shirt: A light fleece jacket, or a synthetic blend woven shirt works well.
Shorts: Pockets that Velcro closed are useful. Belts can get in the way of your hip belt on your pack. Synthetic materials work well for shorts. Long pants with detachable legs, which convert the long pants to shorts are very practical.
T-Shirt: Again, synthetic works well, as it dries quickly. I will probably not carry an extra short sleeved shirt. I will have a long sleeved shirt to change into when we get into camp that will also be what I will sleep in, and on the last day I might hike in it.
Long Underwear: Light to medium weight can be used to sleep in if it is really cold or layer it under other layers
Hats: A sun hat with a full brim. Most of your body heat is lost through your head, and having a warm hat can make the difference for a good night's sleep. I have a knit hat as well as my sunhat with a full brim, but depending on the forecast, a warm hat may not be needed.
Warm Jacket: Pick something that will layer under your rain jacket and over your other clothing. A down jacket or a synthetic fleece jacket are good suggestions. I recommend against cotton sweatshirts, because of their bulk, weight, and they take almost as long as denim pants to dry. A lot will depend on the weather forecast closer to the time.
Underwear & Socks: Synthetic is recommended for underwear due to its wicking qualities. Quick drying socks are something you need to experiment with while you are breaking in your boots. A liner sock is a good idea. They are very thin, made of either silk or synthetic, and help wick moisture from your foot and also help prevent blisters. The outer sock rubs against the liner sock, instead of your foot. Wool, wool-synthetic blend or synthetic are good choices for the heavy socks. Cotton socks tend to hold water and also tend to compact and loose their cushioning benefits easily. You can hand-wash socks on the layover days. I sometimes use knee high nylons for my liner sock.
Camp Shoes: The purpose of camp shoes is to have something to put on in camp to rest your feet. To protect your feet, I recommend closed toe shoes. I use a pair of crocs that I bought at Walgreens for less than $10. If you bring sandals or Tevas, the Sierra Club requires that you use closed toe shoes while cooking, so you will have to put your hiking boots back on.
Hiking boots or shoes: Over the ankle hiking boots are recommended, but not required. I have not seen any solid studies that prove that they cut down on ankle sprains, but many people believe that they do. I use both styles depending on the terrain and the number of miles per day. I do like the waterproof feature allowing me to walk through a puddle or a rain storm without getting wet. Non-waterproof shoes are often mesh on top which allows more air circulation, but wet feet can be cold and more blister prone.
Light weight or disposable camera
Hiking Stick(s): One or two hiking poles can help with balance. For those of you who have knee trouble, they are a great help. I use 2 hiking poles when backpacking. I like the kind that has a little bit of shock absorption to them.
Biodegradable soap and towel: Every night we plan to be camped near a water source where you can wash off the trail dust. However, if you want to be able to fully clean up, you may do so by carrying water 200' from the water source and taking a "sponge bath" using biodegradable soap. Use your bandana for a washcloth.
Water filter: We plan to treat water with water treatment tablets. I will have a filter along to allow you to see how this option works before you decide what works best for you.
Pillow: Don't bring one. Use a stuff sack, and put some of your clothing inside. There are backpacking pillows and for some people, this can be the difference between feeling rested or not.
The backpackers credo is the less you take, the less it will weigh, and the happier you will be!!