After reading all of these answers, I feel like I'm going out naked. When I was in the military, I learned to dislike a backpack with a vengence. Although I still use all issue gear except my boots, heres what I carry:
Bdu pants with small pocket knife, spare batteries, Toilet paper, 550 cord, car keys, handkerchief, wallet, change, a pistol belt with 2 canteens, one with water and the other with Gator-Aid, a survival knife (firearms are prohibited in some areas), butt pack with a 2man first aid kit, poncho, spare socks, extra latex gloves, small flashlight, small swag items, zip-lock bags, waterproof matches, energy bars, 2 civilian colored smoke bombs (just in case), sometimes a 2 way radio. All this is held up with load bearing suspenders, (so my pants don't fall down) that carry my cell and a presure bandage. All this is topped off with my walking stick, leather gloves, Garmin map60Cs and a hat. But, I may sneak a Beretta .22 and ammo in an M-14 mag pouch.