bring your documents and the clothes on your back if you are going to benning. They are going to make you rebuy everything. If anything bring a disposable razor and a tiny thing of shaving cream travel toothbrush and toothpaste. Don't go buy new running shoes or anything like that. The lighter you travel the better. I promise you that doing so will make the shark attack go SMOOTHER...not easier...but smoother.
I bought running shoes to BCT. They were the Asics GEL-Nimbus series. I did not have to re-buy running shoes. That's an extra $70+ on your government issued debit card.
Do bring extra underwear just in case (you sh*t yourself on the way to CIF).
Depends on the DS who is walking you through the reception process. I was forced to buy shoes at Sill and was told at the end of it during the sensing session with the CSM that we never had to. I then went through reception at Leonard Wood for AIT and was forced by a DS to purchase new shoes, again and that I would be "reimbursed". Did that reimbursement ever happen? lol...
Long story short, everything you need to purchase will be sold at the PX at reception. Seriously. Took me two times going through the process to learn that lesson. Everything you need can be fit into a backpack.
Don't buy an athletic supporter unless at reception a DS specifically says to buy one. lol.