The lifeline kits are a good low-cost base to work from - and you can easily supplement them by adding stuff you may want by a quick trip to a pharmacy.

The way I did it was to figure out what I wanted to have the First Aid kit address: I split it up with a boo-boo/ouchie kit (based around a commercial lifeline first aid bag) and a full up trauma kit based around a condor emt bag - with essentially the same stuff as in my boo-boo kit supplemented with israeli bandages, quik-clot and other fun things.

The Boo-boo kit rides in my gearslinger and is always around, the trauma kit stays in my car for the most part.