I don't think I would take any electronics...the whole point of "camps" and camping is to experience something outside of your normal life. I never went to soccer camp per se, but I did play soccer and I did go to cheerleading camp. It's a great time to just live, eat and breathe that one thing, you know?
So for that reason, I would NOT take any electronics or other forms of entertainment. If there are breaks in time there will be plenty of people with the same interest as you to practice drills with, or just sit around and talk about soccer stuff, probably things you don't get to do that much during your regular life. It's a great chance to make new friends who might live far and have a different lifestyle and share a common interest if you're not distracted with toys and stuff too.
ps the only electronic device that I think might be useful depending on the location and your tendency to wander off is something with GPS/compass capabilities in it. I'd leave it off though except for when I'm actually out exploring.
As for food I'd take things that are your personal favorites as well as things you know are popular and would not mind sharing/trading. In every single type of thrown together with strangers situation I've ever been in sharing/trading has always been a great way to get real popular real fast, just don't be pushy, wait till asked or eat something yummy like gummy bears or m&m's in front of others and then share. Your favorite candy bars with energy giving nuts and health bars granola bars, fruit that lasts like apples and oranges, and drinks that don't need to be refrigerated like Capri Sun and Gatorades. Something for the salty and crunchy cravings like chips, rice cakes, crackers, Triscuits and whatnot. Definitely take a couple of Bananas and bottled water...the bananas only last a day or two so not too many but one year at cheer camp a girl actually died from deydration (it was suspected she might have been dieting and it was a very hot summer). The counselors/coaches reminded us to eat and drink enough and it was believed that if she had only just had one banana it would have saved her life, due to the potassium. (sorry to be a downer, but summers are hot and you will be sweating). I'm not a Dr. and neither were they, but it was a stunner when that happened and ever since then I make sure to throw bananas into every summertime excursions in addition to the normal drinks we naturally remember to pack.
Finally, I think I would take a journal also for downtime, not sure where the event will take place but if it's out in nature someplace you'd be surprised the kinds and amounts of ideas that start flooding into your mind when you are in that kind of environment. I think it might just be because your mind is free from the mundane. I remember crushing on some guy who had a real cool leather journal that was more of a sketch book and he used it both to draw and write his thoughts/ideas in.