When you go on active duty for >30 days (your ADT orders are for 45 days), you can enroll in Tricare Prime. For those 45 days you can use an MTF for medical care (you need to enroll at the Tricare office. You may want to send a copy of your orders ahead of time). If you're young and healthy (you generally should be if you're in the program) you might not have a whole lot of need for it, but it can come in handy. More useful is the fact that you will be eligible for dental care. Most schools either don't have or have crappy dental coverage. Your time on base is a great time to get some routine dental care done. If you are doing a school tour, you can still sign up for Tricare (Tricare Prime Remote) and use the coverage. There is dental coverage for those on AD who are remote from an MTF as well. If you have a family you can enroll them in Tricare for the time you are on AD (>30days) by enrolling them in DEERS. There is an active duty family member dental insurance program, but I don't know if it would kick in fast enough for your family to be able to use it during the eligibility period (but it never hurts to ask).
If you wear glasses, go to the base optometry clinic and get a free pair of specs. The new styles are fairly fashionable, and it's always good to have a spare pair. They say only one per year, but when I got to my base I got a pair of specs, gas mask inserts, and a pair of inserts for some sunglasses I bought at clothing sales (the impact resistant tactical kind. You don't buy the inserts at clothing sales; you just tell the optometry clinic what brand/style of sunglasses you bought). You might also be able to schedule an annual eye exam, but they won't do contact lens exam/rx.
Sign up for a USAA bank account and insure your car(s) through them if they insure in your state. Don't buy their roadside assistance, though. AAA is a better deal. When you are getting ready for residency and are thinking of buying a house, strongly consider NOT buying and renting. If you just can't bring yourself not to buy, also be a member of a good FCU (Navy FCU is good) and apply for home loans through them. Long story short, USAA is great for banking and insurance. They suck for home loan processing. But, please, consider renting over buying come residency time.
Uniforms are best bought at a clothing sales store on base or online through AAFES. The same is not true for footwear. You can usually find much better prices on the websites of civilian retailers (I had a good experience with uspatriottactical).
You're going to a branch DO school. When it comes time for picking your rotation sites, try your best to get a site in which most rotations are done at teaching facilities with residencies. I know people will talk about their great preceptor based experiences where they were doing all sorts of stuff as the right hand of the doc, but for every one of those there is at least one story of precepting with docs that really didn't let you do jack. Your residency is an academic environment with a certain structure and hierarchy. By its very nature it will bring in at least some degree of more complexity than that routinely seen by most community based preceptors. If almost all your learning was done in a community based preceptor model, there is a high likelihood it will be debilitating to you to some degree.
I believe, as Perrot stated for the Navy, that all the services use the point system which gives points for published research (I know this for the AF). If you can swing doing some research and can get published do it. Not just for the JSGME, but even for down the line. Establishing (or further establishing) the skill set may help in residency and if you ever desire a fellowship, research experience is a great thing to have. Unless it affects your grades negatively, there really isn't a downside, other than time commitment.
I really don't know about the whole COMLEX +/- USMLE thing. I think it is all going to depend on what specialty you end up applying for. If you have a strong sense for a competitive specialty early on, talk to some of the PDs in that specialty for a sense of whether you should take both exams.
Back to financial related topics: TurboTax is great.