If you have a varied repertoire you can respond to the night. When I sang regularly it was easy to respond to Canadian, American, French, OZzie, Kiwi etc visitors to the club.
It gives you a reason to sing a particular song and draws in the visitor. It makes the evening more inclusive.

As to what songs to learn - chorus songs are always good (inclusive again) choose simple choruses. Comic songs are useful if you have to follow a bad sallad.

But do learn them, reading off the page leaves you little room to "act" the song, and to project you should be looking up at the back of the room not down at the page.

good luck and report back with your choices.