"Down by the Water" by the Decemberists is fun to play.

Check out Tyler Childers. I play his Hard Times at open mic. I also play Everybody Knows by Ryan Adams, Blue Spotted Tai by Fleet Foxes, Cover Me Up by Jason Isbell, New Madrid by Jeff Tweedy. Not a lot of people know these songs but they usually go over pretty good. Incidentally, I see your from Fryeburg. Where is this bar and what night do you play? I don't live far from there. Oh, how about this one.

You need some John Prine

Do a tv theme song (like Beverly Hillbillies) and have the audience sing along!

yes not modern but 16 Tons and Big Bad John

Joni Mitchell

these are songs that my friend performs on ukulele and work pretty well and kind of folky; price tag- Jessie J landslide- Dixie chicks, zombie -the cranberries, soul sister- train, Float on- Modest Mouse, Apple Blossom the white stripes. Given the site, you might try Take Me to Church -Hozier

I can think of plenty - but mostly from British artists that your clientele have probably never heard of.

And I'm sure there are a lot of great acoustic artists over there which I've never heard of too.

You should do a tribute song to the Cranberries since they recently lost their lead singer. That would probably be "Linger" or "Zombie." Chumbawumba's "I get knocked down" is always good..
Len's "If you steal my sunshine" is peppy. Moby's "Southside" if you like a challenge. Blind Melon's bee girl song..."No rain" ...

If you could somehow make Childish Gambino's Redbone work in this style- I would buy a copy from you- even if it doesn't fit this list.

Kelly Clarkson, Breakaway is a favorite.

One I recently stumbled onto Imagine Dragons "demons". Capo 5th fret.....g,d,em,c ....add some fills

Ben Maccallouh by Steve Earl, Undone by Robert Earl Keen, Sunday Morning Coming Down by Johnny Cash.