I've always made it a point to be prepared.  This also includes fire extinguishers and first aid/trauma kits.  In my truck, I carry a self made first aid/trauma kit.  Most first aid kits are loaded with bandaids, lotions and aspirin.  I wanted a kit that was better suited for job site or outdoor injuries.  Like injuries from livestock, chainsaws, job site tools, gunshot or knife injuries.  So, I put together a hybrid kit that has bleeding care supplies (clotting gauze etc.), tourniquet, sucking chest wound, splint, eyewash as well as a reasonable set of band aids. 
I need to go through it and see if anything is outdated and needs replaced.  I also need to see what I might want to add, like a blood pressure cuff and maybe some light surgical stuff.
Years ago, when I used to dove hunt, one of the members was a DR and he even packed plasma for the group hunting weekend.  Lots of folks joked about it, but being prepared really isn't a joke.  That same hunter/Dr is on my deerlease and I had him put together a good trauma kit for the deer camp.  I also made every member provide an emergency contact number.
What does everyone else do for first aid/trauma kits?