Gunnar, this is assuming you haven't done boot. Your first concern should be cardio, and strength a close second. Cut back on carbs, but don't cut them out completely, and increase low fat protein intake. Get a medicine ball and look up workouts that incorporate them, if you have a partner even better. You can use it for strength and even incorporate it into cardio, it's a good tool to have for working out.
Start jogging, or if you're already in decent shape running. A good schedule is,
Day 1 - "distance" run: running or jogging at a pace that maximizes distance.
Day 2 - Strength Cardio: push ups, pull ups, jumping jacks, running in place, medicine ball workouts. You can find instructions for these online, the idea is to do sets of these without stopping in between, alternate between muscle groups but try to keep heart rate up.
Day 3 - Rest, or light weight lifting/asymmetric strength training
Day 4 - Interval Training: Look it up, long explanation but easy do understand
Day 5 - Strength Training: You can use weights, or a medicine ball and pull ups, push ups, sit ups etc. Instead of worrying about keeping heart rate up you're worried about pushing the number of reps and form. A slow push up with total control takes more strength that 10 fast half ass ones.
Day 6 - Low Impact Cardio: Best option in my opinion is Swimming, can do a a bike or 'ski machine' also. Some people say jump rope but I think that's too much impact.
Day 7 - True rest, no purpose full exercise. This is also a good 'cheat' day for your diet. A little extra fat or carbs are ok on this day, just don't go overboard.
Do not try and cut calories while doing this routine, you will feel horrible and eventually give up. If you get a sharp or repetitive pain, stop and do something else, and don't push to hard the first two weeks. Also, if you do this for two or three weeks you will lose weight at first, then gain a few pounds in weeks four and five, that is normal. And if you find yourself really low on energy, or getting light headed regular, up your carb intake with preferably unrefined carbs.
Good luck, and enjoy San Diego if that's where you go to camp, and don't try to prepare for the phases. Just be in the best mental and physical shape you can because the instructors job is to break you and then rebuild you.