I used to make my own kits, but I found that EMS has good little kits that seem to work OK for me:

http://tinyurl.com/vxl0

I carry a "Solo" with me all the time, have a "Guide" kit plus Sam Splint in the Jeep and have another Scout Kit in the Wife's van.

I added to the larger & car kits instant ice packs - really helpful with kids.