If you do ANYTHING to prepare for COT, buy your uniforms ahead of time. I spent around 5 hours in AAFES getting uniforms and having it measured for tailoring....and I already had my BDU's. I can't remember the # of blue shirts I had, but I want to say 2 short sleeved only.
Get your uniforms here at Offut and have the name tapes and ranks sewen on before you go, if possible. You'll have an extra 4-6 hours of downtime the second or third day you're there to sit in your room while everyone else is at AAFES. I heard there was a place to rent your mess dress so you don't have to buy it, but i can't confirm that. I'd call ahead on that if I were you. Don't get the regular AF workout gear at Offutt, as COT uses their own stuff, so you'll have to get that there.
And definitely don't take a printer, like the COT website says. If you have a laptop, maybe bring that, but you have a computer in each room that connects to a floor printer. May be smart to bring a little computer paper, though.
If you are still in town and need help at AAFES here at Offutt, shoot me an email and I can swing by to help as much as I can after clinic.