Or just overnight. I've found that the gear is the same, except for food. Even if you just go overnight, you need:
Shelter (tent for me)
Ground cloth (some feel this is unnecessary)
Food (never unnecessary)
Cooking gear (unnecessary for some lightweights who save the weight and eat cold food)
Extra clothes, especially socks
Light source (headlamp, flashlight, whatever)
Sandals (to wear in camp, get out of those hiking shoes)
Cell phone (which may not get signal)
Really.... you need ALL this stuff for overnight. Only difference between overnight and long hike is in the amount of food carried. For the AT, I'm figuring on about 5 days' worth at a time, to last me till the next resupply town/crossroads.
I should detail every aspect of my pack in a separate post, and probably will.