I carry the Park GP-2 self-adhesive patches, and a couple packs of alcohol swabs to clean the tube before patching.
If you can locate the leak, it is possible to just pop off one bead, pull out the tube and patch it, w/o even removing the wheel or tire.
It is rare to not be able to find the leak.
When I get home, I swap out the tube, then replace the self-adhesive patch with a permanent patch.
The self-adhesive patches will eventually start leaking.

I also carry a spare tube and boots for flats with damage greater than a simple puncture.