Learned/first tried this at an OS workshop:
Tie a medium band (or two medium bands end to end to increase the length) to a KB.
Loop the other end of the band(s) behind your head and crawl backward, dragging the KB along the ground.
This forces you to keep your head up, your butt down and extend your t-spine, which lights up your whole mid and upper back, and the added resistance to backward crawling lights up your delts (in addition to everything else that crawling normally lights up). This is a super drill for posture and has a surprising carryover to shoulder function and overhead lifting.