For acoustic gigs, it's usually a pack of strings, a few picks and a strap in the case. I carry a backpack with a stand, a couple cables, tuner, battery, capo, slide.
For a jam with an electric, I'll throw in a couple cables, tuner, maybe my AC Booster, picks, strap, strings.
Band practice or small (non-paid) gigs, between gig bag and pedalboard bag I'll have a few cables, power cord, extension cord, picks, capo, slide, strings.
For a "real" gig, I bring the above plus a small tool box with screwdrivers, allen wrenches, extra tubes, duct tape, etc.
Oh! And earplugs. Always have my earplugs!