well it all depends on how good the high school is that you are going to. some freshman teams i know are better than some varsity teams.
one thing that you have to do at tryouts, is get yourself noticed by a coach, IN A GOOD WAY! always be there to volunteer when they need help, dont EVER walk, always jog, run, hustle! wear a bright colored top, that will also get yourself noticed.
also, each day for the camp is different. but here are some things you will be doing at the camp, but i dont know the order you will be doing them in:
meeting about volleyball and high school volleyball (always first)
seperate people on courts by how good they are (daily)
serve, hit, pass, set(daily)
scrimage(few days out of the week)
cut people(??? how often)
and here is a checklist of things you will need:
1. Hair tie/clips/head band
2. workout shirt (normal t shirt. dont wear a spaghetti or noodle strap shirt. coaches hate that. its for players who dont really know what they are doing and havent played for that long)
3. spandex
4.kneepads
5. (if needed) ankle braces
6. running shoes
7. water bottle(s)
8. bag to put stuff in (optional)