You can airplay to a Mac or Windows PC using a variety of programs available from 3rd parties. I can't tell you which is best, but I seem to recall "Reflector" and "AirServer" as being well known.
There aren't any good solutions to AirPlay to another iPad or iPhone. There is an App you can side load, or there are some jailbreak techniques, but they all seem sketchy.
Then there is this:
https://smile.amazon.com/gp/aw/d/B01DLFQYC8/ref=ya_aw_od_pi?ie=UTF8&psc=1
I just ordered a couple. In theory we should be able to stick these into the HDMI port of any monitor/TV and airplay straight to it. So you could bring a high brightness 7 or 8 inch monitor out in the field with you, stick this in the HDMI port, and airplay to that. That's what I'm going to test.