I sometimes call at a club where numbers are thin at the start and I can't start with a longways dance. So I look for 'elastic' dances that can accommodate low numbers that vary during the walkthrough.
I find that there are several dances that are officially 3 couple but will stretch with a bit of improvisation.

Epping Forest and Jovial Beggars are circle dances (Playford type) for 3(ish).
Upon a summers Day is a Playford longways for 3, if you have more than 3 you can either play the B music more times or start part 2 with a different couple at the top.

Rufty Tufty, Hit & Miss (usually danced to tune Daphne), & Heartsease are Playford dances for 2 couples and Dorset 4 hand reel and Hullichan are lively ceilidh 2 couple dances (some older folk don't like it). I was thinking last week that Rufty could be done as a 3 couple circle.

Ploughboy is a good 3 couple longways. Gypsy Hill Jig. Bonny Breast Knot - Somerset and Devon version, Shrewsbury lasses, Bishop, Fandango.
I think a lot of these were originally longways triple minor dances, i.e. danced in groups of 6 down the set. Most of them have a set tune.