One thing most people bring that I've never found I needed is a sleeping bag. Sweatshirt, sweatpants, pillow and sleeping mat for sleep. If it's not a lot of floortime I just grab my pillow (that's already on the bus) and grab 30 minutes of sleep while everyone else slaves over inflating their beloved airbed (I use a normal Boy-Scoutish airmat). If there's more floortime I'll get it out, but honestly I'm always tired enough to be able to fall asleep without being 100% comfortable.
Bring a power strip with your chargers electrical-taped to it. Write your name on a little duct tape flag, so if you ever leave it in the gym the drumline (or whoever cleans up the gym in your corps) knows who to give it to (I know I'm fairly merciless in throwing unlabeled stuff away when in a rush to clean up).