Of course, with all the other great advice you will get, be sure to bring extra spokes. You can tape them to one of your seat stays.

Also, bring a good first-aid kit. I like to make my own to be sure it is specific to the types of injuries common to bicyclists. That means getting some good topical pain relief spray or ointment and road-rash specific bandages.

Shopko sells disinfectant wipes in individual single-use packets. I have used these quite a bit. They clean and sterilize the wound.

By the way, this may sound weird, but one of the best road rash bandages you can get is a thin but large feminine napkin. They are clean, convenient, absorb a lot of blood, and are wide enough to cover a bad road-rash wound.

Also, a small bottle of the convenient "no-water needed" hand cleaning gel is very useful. You might chose this over the towelettes if space/weight is a big concern.