Just stating the obvious...
1. head & spinal trauma
2. how to temporarily set broken bones
3. dealing with open wounds & gashes
4. dealing with shock
having a first-aid course dealing with common injuries associated with biking injuries, is a great idea. the next step is convincing someone to carry all the equipment...better yet, how improvise in certain situations. As yet, I haven't been able to convince anyone to let me stitch them up( I have 4 different suture kits in my med pack). I highly recommend this book, in a first-aid kit(mine came with).
http://www.rei.com/search?query=wild...ravel+medicine