I have a bp drill that allows each kid to get 16 live bp cuts, 16 t cuts, 16 soft toss cuts, 16 fly balls/ground balls (depends on if you're a inf or outfielder) and their sprints in (as the shag).
A twelve player team can finish the entire thing in 35 minutes (as a pregame bp). If you don't want to rush it's easy to finish in 45 minutes.
I detest the standard "stand around" bp with one kid hitting and the rest shagging. I mean........talking about who they're shagging.
Complicated to explain but very easy once you get the hang of it.
Need 3 Coaches and 64 baseballs.