Like I said before, the little PX has most of the things you need for TBS, as well as at the mainside MCX. Also on Camp Barrett is a slightly larger MCX convenience store. THIS IS WHERE YOU GET YOUR LIQUOR!!!! The tiny PX only has beer. This one is located at the intersection of MCB-1 and MCB-2, near the fire station.
Two things you will definitely need for TBS:
PRINTER
LAMINATOR (with laminator sheets)
If you know your roommate ahead of time, I would split the two among yourself. Even better, if you know some Lts from the company before, they will probably be more than happy to hook you up. You will use your laminator for SO MANY THINGS.
The little PX has MCMAP belts, green skivvy shirts and shorts, socks, etc. They have most things for the field as well that you are not issued, like flashlights, map pens, batteries, etc. It was actually pretty decent.
You will be issued two maps of TBS, don't lose these! You can take these to the little PX to get laminated.