I attended USAFA SS session #2 last year and it was a blast! It was awesome because the whole event is a lot more laid back than the actual academy and the cadre (element leaders/currrent cadets) are there to simply answer any questions you have. There are not mean to you like they will be at basic, so like said above, take this time to ask AS MANY QUESTIONS AS POSSIBLE!!!!
The biggest piece of advice I can give to you is to not be the person who thinks they know everything. I have a brother who graduated from the Academy and have been there many times, so naturally I wanted to be the guy who would be the bastion of knowledge. However, after an hour being there, I realized I only truly knew a fraction of what there is to know about the Academy, and I chose not to be that guy. Of course, there was a person who had been to all three academies' SS's and he decided to be that guy. He also ended up doing 80 pushups with 8 Cadre in his face during PT every morning becuase he wouldn't shut his mouth about all of the 'experience' he had. Just have fun and listen to all the advice and stories. It really is a good experience.
Workout, workout, workout! I love running (distance) but I was out of breath after a mile, and so was everyone else, even track athletes. If you get discouraged from the exersize, remember that everyone else is too.
They give you a buch of stuff so dont overpack. We got two pairs of workout shorts, four workout shirts, a windbreaker, towell, polo shirt, backback and really nice binder. Bring good exercise shoes and dress shoes as well (for the final dinner). Lots of socks. I wish I would have brought compression shorts, so bring those too.
Get to know people. I still talk with the people in my element to this day and we had a great time becuase we always worked as a team. Nobody fought, ever.
Have fun in the classes, do not take them too seriously. The point of them is to give you a little idea of what the departments at the academy are like, not neccessarily the classes. The proffessers (at least the ones I had) were awesome and loved to answer questions. Ask lots of questions and have fun.
Remeber the whole point is to make you decide whether the Academy is for you or not. I loved SS and it made me excited to go to USAFA. My friend hated it and dropped his application immediately after getting home. With that being said, go in with an open mind and just try to experence as much as possible
Good luck and have fun!