My son packed light to attend Beast, but he did pack moleskin, blister bandaids, extra socks, a couple pair of compression shorts, and cushion insoles. We sent him several packages after Beast started which included more socks and more compression shorts (black).
Try not to overpack ... keep in mind that you will have to carry this bag around for quite some time, then transfer the contents into the issued bag.
Properly fitting footwear is the best defense against blisters. Make sure they don't slip, or that they're too tight. Once you purchase the low quarters and boots, wear them so your feet get accustomed to them. Take long walks around your neighborhood or wear them to school here and there.