>> “The best field-expedient treatment for asthma I know of is hot, black coffee.” <<
Don’t know ‘bout that, but if you live in the eastern half of the US, the best cure for asthma, and any other restriction of the bronchi, grows beside almost every road: Lobelia.
A plant with a pale blue to white blossom, and bladder-like seed pods (hence its slangular name - “Bladderpod). All you need to do is chew up some seeds, which will temporarily cause a scratchy sensation in your throat, and shortly after complete relief of the bronchial tightness.
No side effects either, (except a slight reduction in blood pressure for some) unless you consume pounds of the stuff.
Huh - never heard of it. Does it grow in VA?