I've tried using the "back pocket" approach a few times, but i always end up needing something i don't have.
I wear a tool belt 99% of the time. 4" small tip, 6" large tip screwdrivers, ratcheting screwdriver w/philips and spare bits in handle, channel locks, klein 2000 linemans, 6" needlenose, diags, wire strippers, utility knife, 6" awl, tape, fluke non-contact tester, tape measure, hammer if I know I will need it.
To help balance it out i have a 4 pocket nail pouch on the other side. Wire nuts (twisters & greenies), staples, misc. screws, sometimes a romex connector or 2 depending on what i might be doing.
Suspenders to keep it all balanced.