A small container with a pull-tab; pulling the tab ignites the thermite charge which pops the popcorn above it which then pushes off the lid allowing it to expand into a large paper or mylar bag.

//Quick ... very quick.// But perhaps not quick
enough. Instead, what is needed is popcorn with a
tiny detonator set in a half-millimetre hole bored
into the kernel. All of the several hundred
detonators are wired to a common source for
_truly_ instantaneous popcorn.

For an additional cost, the detonators can be
individually connected to a 500-terminal control
box, allowing a detonation rate that matches the
consumption rate.

// I'm afraid there's only one solution that would match 8th of 7's consumption rate. //

You are correct. Be afraid... be VERY afraid...

// U235 //

No-one's built uranium devices for about sixty years. They're baby-steps things. All realistic gadgets are Pu-implosion, axially symmetric using pusher plates, and then fusion-boosted.

//All
realistic gadgets are Pu-implosion, axially symmetric using
pusher plates, and then
fusion-boosted.//

I believe that from this statement (and a few assumptions)
we can calculate the Borg's
appetite for destruction - to a first approximation.

Apparently popcorn kernels pop at somewhere between
180 and 232 degrees C. Let's call
it 220 degrees C. Let us suppose that the initial popcorn
temperature is 20 degrees.
So I found a table on teh internet which suggests that
popcorn's specific heat is around 2
kJ/kg.K (2.04 air-popped, 1.99 oil-popped). We need to
heat it up by the difference of
200 degrees, so that's 400kJ per kilo.

For the yield of the gadget from a fifth-rate dictatorship, I
propose the yield of Ivy Mike
(10.4 megatons TNT) as a reasonable approximation, where
a Mt is of course 4.184×10^15
J. This gives an amount of energy available of about
4.4×10^16 J

Then we can divide through to get around
1.1*10^12 kg, or 110 megatons
of popcorn, assuming 100% efficiency. In practice I suspect
that a yield of 1% of that (a million tons)
would be considered sufficient, and leave enough space
around the fire for the borglings to roast
marshmallows, and perhaps horse-chestnuts.