Toilet paper. Scissors to cut hair/trim beard. Tweezers. Butt-loads of wet-wipes.
Outside of that, some form of entertainment. Books, porn, boardgames, deck of cards... whatever floats yer boat.
We always think of the "action" involved in a SHTF situation. Attackers, securing a food/water source, etc... But the fact is, once you reach a safe area and hole up, things are gonna get real dull, real quick.
Five things that will seriously ****** with your head;
5) Sheer boredom.
Oh, and a pillow. A pillow would be nice...