For us, playing pubs with a vocal-only PA, soundcheck - two verses and choruses of a song using BVs. Checks that the vocals are balanced and the instruments are balanced with each other and the drums. Seeing as most of the time we have to eject people from their seats in order to set up, we're never going to get to soundcheck in an empty room. And we do a song that everyone will know and we do well, so those already there may have their interest piqued enough to remain (unless they're sulking at being ejected from their seats).