my list:
1. comfort
2. stay warm
3. have something to eat
4. mental aspect. I think staying all day is mostly a mental game. The one thing that I do is decided BEFORE I go out that I'm going to sit all day. If I decided to see how it goes in most cases I won't stay all day. It can get tough because I hunt areas with very few deer and I have sat all day many times without seeing a single deer. It's tough to sit all day and not see a deer!
5. All day sits are tough. It's not for everyone. There is no way I would do it every day. Hunting is supposed to be fun and I mix it up a lot more now days.