bare essentials

just a tip from a young guy that might just save your skin someday. From the day i was old enough til now I've always been involved with scouting. Im an eagle scout and have had the opportunity to teach the wilderness survival merit badge quite a few times and also lead a trekking program over the past 5 or 6 summers. I've always loved wilderness survival and even made a few "survival" trips myself. whenever i head out in to the back country or even climb in my truck i at least have a few small things with me. in scouting its called the 10 essentials and I'm sure that a lot of other people and organizations have adopted and adapted them.
1. Fire starter (usually matches or a lighter. a lighter is easy to use convenient and can pick one up for a buck at any gas station anywhere. they do run out of fluid faster than you think and once its out, its out for good. matches are good as long as they don't get wet, even the waterproof ones. the match head might me waterproof but if the wood gets wet you only have a few split seconds to get a fire going. if you're going to use matches, I've found the "weather-proof" ones to be the best. the match head extends almost the whole length of the match and they're windproof. Flint and steel is pretty intimidating to master but if you get good with it, it will last darn near forever and is completely weather proof.)
2. map and compass (can't get lost if you know where you are. GPS is great but like a lighter, once the batteries are dead, they're dead. a map and compass will never loss reception or run out of batteries. you'll need a good topo map, its better to pony up and buy one rather than print one off the internet. the lines will usually come out blurry and skewed, nothing more frustrating than to try to read a low resolution map at night. if you can get a waterproof one then get it! rain, snow, lakes, rivers and mud are all enemies of a good map. Get a good compass too! the little keychain ones on survival whistles will do in a pinch but spend the $20 and get a decent silvia or military surplus one)
3. trail food (protein bars, trail mix, jerky, something packed with a lot of protein and nutrients)
4. water (DUH!! iodine tablets work well just be sure to try them out before you hit the trail. don't want to have a bad reaction and be dehydrated. water purifying pumps are awesome, just be sure you know how to use it. bring a bandanna or handkerchief to pre filter in especially swampy or gritty water)
5. Sun Protection (one word HAT!!! a hat will keep the sun off your vulnerable face and if you're walking away from the sun, flip it around to protect your neck. a baseball cap will work just fine, especially in strong winds. a full brim boonie hat or cowboy hat is even better especially if it has a lanyard to keep it from blowing away. sunscreen is good too if you don't mind a couple extra ounces.)
6. Rain Protection. (poncho, poncho, poncho. military surplus ones are a bit bulky but can double as a rain fly in an emergency shelter or that darn ground cloth you forgot to pack. not to mention you can collect rain water with them. the smaller disposable ones are good if weight or size is an issue but won't put up with the abuse that non-disposable ones can.)
7. First aid kit. (small enough to not be over bearing yet big enough to attend to the group size that will be with you. make sure it at least has the basics. moleskin, bandaids, gauze wrap, scissors and tweezers. an ACE bandage or a bandanna and duct tape is a big plus)
8. Flashlight (headlamps are great but i also like to carry a small handheld also. don't forget spare batteries! try putting electrical tape over the terminals of spare batteries and batteries stored in flashlights to keep them from grounding out and draining when not in use.)
9. Extra colthing. (pretty self explanatory. bring socks at very least! also i like to keep them in a trash bag or some kind of dry bag just in case my pack decides to go for a swim or it starts to rain.)
10. Pocket Knife. (probably the single most useful tool you can have with you. i usually have at least 2 with me. 1 for around camp tasks, cooking, opening food packages, opening bear cans cutting line, making kindling etc. and 1 large knife for heavy use or as a "survival" knife. also a kind of handy to have a multi tool with you. a knife is going to be without a doubt the most used tool you will bring with you whether in a survival situation or just day to day activities. be prepared to spend good money on it. folders are handy usually light weight and compact, a locking blade is an absolute must. sheath knives have their place and are well suited to hard use. you'll want a full tang and a thick heavy duty blade. smaller sheath knives may not be as practical as a good folder but are usually much more durable. its all personal preference but whatever you get, get the best.)

rope, trash bags, duct tape, a few fish hooks, the list goes on and on from there. carry what you see fit but make sure you at least have these 10. the key is balancing quality, usefulness and size. you can buy micro compasses, small LED flashlights, small packages of band aids but keep in mind your life might depend on these items. a few extra ounces for something of much higher quality or will be more useful is well worth it, just make sure you're not adding so much weight that you won't carry it everywhere.
Hopefully none of us will ever have to use our survival kits for its intended use but if the time comes that you have to, be prepared!