I tend not to take many of the essentials. At first, because I was young and dumb and fairly tough. Now, because the 8x10 and age determine how far I can get away from the car...but I do tend to go off in weird directions by myself, tempered by having a good sense of knowing when to turn around (I chicken out easily, but I still get to some cool places.)
But there is room for some emergency food in the pack -- a few food bars, an apple, turkey jerky, and perhaps some of that wonderful new survival ration, micro-brews in cans (always room for a couple). And I always have my rain jacket/hood, and a wool cap in colder times. I love topo maps, so that is more than just an essential. But oddly rarely have a compass -- the sun and terrain tells me how to align the map, weather and cover permitting. I might take the water filter and only a partial bottle of water if I will be out all day and near water through out the day. A flashlight should live in my camera pack, but one doesn't. A Leatherman tool I found along a creek is usually in the pack (I often need to tighten a few screws on the 8x10) as well as a lighter. A needle and heavy thread usually are with me on long (week+) hikes...I have had to do some major sewing on equipment. Those old Kelty Tour Packs were not designed for the weight I use to put in them!
But if I am just going out for the day, I might as well toss in an extra couple 8x10 film holders (6 or 7 total) and pull out one of the external pockets of the pack to put in a sandwich, another apple and perhaps another can of beer. So it is no wonder I only get a few miles out before the 45 to 50 lb pack and 17 lb tripod/head point out that the light right here right now is beautiful and I should set up the camera, expose some film and drink a beer...if only to reduce the weight of the pack and to enjoy where I am at (oh -- and to rehydrate, of course!)