Welcome to SC!
Here are a couple of things that I do during my commute every day:
Butt clenches - I do 1 group of 30 fast, then 1 group of 30 slow (holding for a couple of seconds each time)
Abs - I tighten my abs and hold them tight for 10 seconds, release and repeat (I had to work up to this)
Kegles - I do groups of 10 fast, then groups of 10 slow
I know it doesn't seem like much, but every little bit helps
