This is a sample list of things you might take on a week-long trip hiking in a wilderness area. Even more than with other kinds of travel, packing for this kind of trip requires compromises between keeping weight down and making sure you bring everything you'll need, because you have to carry it all with you. Depending on where you're going and the time of year, some of the items may not be useful to you, and there are inevitably additional items you'll want to bring along, but this should give you a general idea of what you'll want to pack. (Please keep in mind that we want this list to be useful to people in general, so don't edit it for your own specific needs.)
Remember, cotton is usually called "death cloth" by park rangers for a reason. It soaks up water many times its weight, and hence its drying time is very slow. You're anywhere but a desert - and even then - be sure to wear mostly synthetic fabrics and bring a waterproof windbreaker to avoid hypothermia in rainy situations.
2 undershirts - go for synthetic here. You're gonna sweat through them, so pick something that wicks. Capelene is a good bet. Many discount stores will also sell suitable shirts in their sports department if you don't want to drop the money.
2 long-sleeve shirts - again, go for synthetic.
2 tshirts - you don't want to sleep in your sweaty undershirt. If they're layered over a synthetic undershirt and and with a long-sleeved synthetic overshirt, these can be cotton.
2 pair of pants (suitable weight for current weather) - hiking pants that zip off at the knee are a invaluable.
2 pair of underwear - make sure they wick away sweat.
2 pair of wool socks - spend the money for good hiking socks. Your feet will thank you.
hiking boots - stiff soles and plenty of ankle support are a good idea if you're going over any rocks. They'll also stop your feet from hurting, and can posibly prevent you from twisting an ankle. Do yourself a favor and break them in beforehand by wearing them around for a week. Then you'll know where they rub, if you want to put soft insoles in them, etc. They should conform to the shape of your foot, so by the time you're ready to hike, your boots are too.
sandals (for wearing when not hiking) - unless St. Patrick drove the poisonous snakes out of the area, don't wear them outside of your tent. First aid for snake bites is no fun, and if you can't identify the species that bit you, it's best to err on the side of caution.
hankies - sneezing? bleeding? need to collect berries? Hankies are worth the extra ounce in your pack.
waterproof windbreaker, or at least a jacket.
raingear - ponchoes can drape over your pack and save you the expense of a waterproof packcover.
swimsuit - bring the one piece.
Women only: two sports bras - spend the money and get the good ones.
oatmeal, cereal bars, trail mix, sausage
gas camping stove, matches
dish cloth, scouring sponge
multi-tool pocket knife (e.g. Swiss Army or Leatherman)
plastic bag for trash
foam or air mattress
travel pillow - many you can buy at hiking stores collapse into a tiny pouch and worth the money. It beats sleeping on your synthetic shirt.
headlamp or flashlight, new battery - in fact, it's best to bring extra batteries, just in case.
maps, compass - make sure you can read them before you set out.
hiking staff - with a heavy pack, these become godsends after hours on the trail.
Stay healthy and safe
sun lotion - nothing's worse than a sunburn to raun a good vacation. Apply early and often.
a hat - one that shades your face is best, and remember that if you're cold, you lose heat through your head. Cover accordingly. A warm head can make all the difference on a cold night.
light trekking towel, bioshower-soap - like the hankie, you can use them for anything.
blister care (e.g. moleskin, adhesive bandages)
cash, bank card
something that can be used as a bandage (hankies work, but for the nicks and small cuts, bring along some Bandaids).