My Two Cents:
Running shoes, mostly (85-100%) black OR white. There's nothing like paying $75 for a $25 pair of Asics at 30th AG BTN (or equivalent). Make sure they are new! Your reception DS's will check the wear.
Every cycle there are recruits that for some reason decide not to bring a cellphone, or no charger. Bring your cellphone AND charger, no question. Plus your debit card.
Shower shoes can be bought for cheap at reception. Stamps and envelopes can also. Buying the smallest denomination calling card is also a good idea (some companies prefer to allow payphone use versus cellphone use), buying the smallest denomination will allow you to figure that out without wasting money.
There's more than that, but it should be on your packing list within your $2 army strong backpack. Those are just things I wish peopel told me.