Hi Meril,
I know a lot of folks here are telling you that they were miserable in camp as a kid, but I personally had the exact opposite experience. My parents didn't send me to camp for years, but I asked if I could go for the first time the summer I was 11 years old. I was SO nervous. I always did love going outside with my parents and camping with them from time to time, but this was a whole new experience for me to be away at camp with people I had never met before. Well, to make a long story short, I loved it. Thanks in part to my childhood summer camp experiences I realized that being outside as much as possible was the way to a happy life for me. Today I am a field biologist by profession.
Now, this isn't to say that camp was all smooth sailing. I found the following things to be annoying about camp:
1. It's not just you who has trouble going to bed at night, other kids do too. Unfortunately some kids are very annoying and like to stay up talking or even singing to themselves (for attention I suppose). I advise you not to throw shoes at them. I found out that this is a good way to get in trouble at camp.
2. Some kids are going to want to be your friends and some kids won't. The good news is that there will be SO MANY kids at camp that don't know each other yet, that your bound to at least meet one or two people who will be interested in befriending you.
3. Sometimes it's hard to just let-go. Going to camp was very good for me in part because it made me change my routine. Going to a new place and bringing a bubble of safety is comforting, but it can also take away from the experience. If you need your ipod yes, find a way to bring it with you. This I understand. However, I urge you to try a night going to bed without it, just to see what it's like. I find the quietness of the forest, sounds of rain, and morning birds, to be quite comforting and nice to sleep to. Maybe you will feel differently, and that's ok too. I just really enjoy sleeping with nature sounds around me.
4. Other people controlling my meals. I was a grazer as a kid, eating constantly in small portions throughout the day. It was really hard for me to change to the system of cramming HUGE amounts of food into my gut at three wide intervals and then going right back to physical activity. Maybe this is just me.
As for your guitar, bring it if it's something you'd like to share with your friends. If you feel awkward about it though, you can also leave it at home. It will be there waiting when you return.
And for bunks, I always choose top myself, but for absolutely no good reason. I think it just makes me feel safe being high up, like a cat or something. I'm sure this is just personal preference.
As for down time, they gave us some (maybe an hour or two a day) at my camp. If you need more, that is a good thing to contact the camp about ahead of time too. IMO the more communication you can have with the camp counselors about your needs, the better.
Good luck at camp! Have fun!