Crazy, out of the box abstract thinking here, but explosives are just highly volatile chemistry. Batteries are all about galvanic potential in slightly less volatile chemistry. Batteries were developed for life cycle reuse. For drones, surely some chemist out there can think of a way to make a single use battery that is also an explosive. Perhaps one that has the structure to mount a small electronics kit with a few motors.
Maybe as a fire starter you could short the terminals or the plates/cells with a spike.
Most expensives work by rapidly generating a large volume of gas in a compact area. The rapid expansion of the gas creates a Shockwave that can be used as a concussion blast or break about the bomb housing to throw shrapnel. Not really anything close to the same reaction. But this is all kinds of explosives...
Hmm. I suppose that that's probably the easiest way to get a maximally-light casing -- it's a thin aluminum skin and available in a standard size in large numbers.