Warm clothes. Packing layers would be best so you can dress appropriately no matter what time of year you need the bag (summer vs Winter). You don't want to be packing your bag when the shtf.
Also Ammo. For whatever your carry gun and/or rifle you will be bringing.
There are also other considerations based on where you are bugging out to. Another house or will you be roughing it (camping, etc).
I'm sure there is tons of other stuff I am not thinking of.