Depends what you want?? For drill, I use drill book. Pretty cool app lets me put in my coordinates so I don't have to carry anything but my phone on the field.
If you want scores I have DCI scores and WG scores.
I have a couple of metronomes and tuners
Best corps app is for Madison Scouts, but Blue Coats, Phantom, BD and Cadets also have pages. Scouts is best because they have recordings of their shows since like 1953