If you really want to learn/do some important stuff before starting UPT that will be 100% useful. I would taking care of the following 3 things.
1. Investing. TSP, Roth IRAs, allotments, etc. get smart on ALL this stuff and put a plan in place to start saving money now. Best advice I ever got was to set 100% of my incentive pay(flight pay) into TSP 6 months before I even started getting flight pay. Now it is all going towards retirement, as well as maxing my ROTH IRA, and I don't miss a penny of it. Even doing all that I am still able to buy as much beer as any other Lt. out there.
2. Education. Knock out 3 or 4(or more) masters classes while you are on casual most places give you a 7 year window to complete the degree, or at least embry riddle does and they have an office at every AFB I have ever heard of. Also, get smart on the post 9/11 GI bill. This is a huge benefit that if used well could be worth over $100,000 of education for either you, your spouse, or one of your kids.
3. Get in shape if you aren't already. If you are only in semi-decent shape now odds are you will be in horrible shape towards the end of phase 3. That said my squadron DO said yesterday, "We will not graduate a student that can't pass a PT test." Make damn sure you aren't that guy/gal. My first week at ASBC I saw a girl get sent home for not passing the PT test...how will that affect her down the road I don't know...but I am sure it didn't help her any.
Just my $.02 but I see tons of my peers who aren't doing those above three things, and those three things are what will put you heads and shoulders above your peers in both your career and life in general.