Well, you probably have heard the old saying, "If you can't play something good, play something we know."
Decide if you're going to do covers or originals. I presume by asking here that you're talking covers.
I like 1970's era folk/pop music and country music. So my answers will go in that direction.
James Taylor stuff - easy to mix it up, old or new. If you need the name of a particular song it's tough to wrong with Sweet Baby James. But you've got Steamroller and a million other tunes. Copperline is another good one.
Cat Stevens - Zero, Father & Son, his cover of Another Saturday Night, plus about a zillion others
Tough to go wrong with John Denver. Everyone knows Take Me Home Country Roads, I'm sure you can get some folks singing along with that. But he's also got a million songs to go with.
I like Land of Canaan by Indigo Girls, but the part I like best about it is the interplay of guitars in the instrumental section, and you'd have to be talented beyond description to play both parts simultaneously. So maybe go with Galileo.
Can't go wrong with Beach Music at the end of summer. Up on the Roof, Under the Boardwalk, 60 Minute Man, whatever.
Have I got to ten yet?
- Zurf