A bandana. and the water in my water bottle. Sometimes there's a couple of band aids in my ID wallet. salt tabs in a glassine bag in my seatpouch.
anything else can
A)wait until I get home
B) buy at the next store
C) ask the guys in the ambulance
The bandana gets used a lot more often for non first aid stuff during rides.
for tours and off road rides I pack a full first aid kit with lots of absorbtive bandages, narcotic meds, EMT shears and the like.
and the most often overlooked first aid items for preventative aid during long rides are sunscreen and adequate salt and water in my opinion.