Green’s Dictionary of Slang

munchie n.1

also munchy
[1950s+] (orig. US)

1. usu. in pl., a snack, snacks or small meal.

2. attrib. use of sense 1 .

3. usu. in pl., the craving for food, often sweet or in an otherwise unlikely combination of flavours, that afflicts smokers of hashish or marijuana.

4. a snack eaten to assuage this craving; also attrib.

In phrases

munchied up (adj.)

[1990s+] experiencing the pangs of hunger that accompany the smoking of cannabis or (occas.) heavy drinking.