when out solo:
look through photos, take new photos, check out exactly where i traveled during the day on the map, plan where i will be heading the next day on the map (i luv maps), nap, read, eat, ponder the meaning of life, write in a journal, listen to music (i don't do this often), watch the sunset, look at the stars, make a fire where appropriate, etc.
when out w/ other people, i do the above plus:
talk, make jokes, tell stories, play frisbee where possible, play cards, etc.
Personally, I like camping about equally as much as the hiking part of backpacking - especially when you are camping at a nice, remote backcountry spot w/ good friends.