What I like to do when I’m travelling/away from the weights:

200 push-ups

200 sit-ups

200 air squats

If you’re starting, you can do 100 of each.

I like splitting it up by doing 10-20 of each (so 10 push-ups, 10 sit-ups, 10 air squats) then 30 seconds to 1 minute break then repeat