The name derives from hip hop. It may also come from resembling a thwomp (rectangular stone enemy character) from the Super Mario series. It takes this appearance when it is tightly packed into a small plastic bag and the edges become ruffled.
(This etymology is missing or incomplete. Please add to it, or discuss it at the Etymology scriptorium. Particularly: “dubious”)
1998 July 21, "TSmith6235", “Re: Those new Partnership for a drug-free America commercials...”, in alt.drugs.pot[1] (Usenet):
However, last night we scored a twomp (20 sack) of this extremely chronic weed, and we hotboxed Shaun's car...I was GONE. Just out of it. Almost uncomfortably stoned.
1998 August 23, Alexander Carlton, “Re: Doser aka A. Carlton vs. WUZ”, in rec.music.hip-hop[2] (Usenet):
[…]twomp is twenty, so a twomp-sack is a 20 sack, generally a tiny bit over a gram of green (prices are outrageous).
1999 February 13, "Michelle", “Re: shitty tips in the past week”, in alt.pizza.delivery.drivers[3] (Usenet):
[replying to: Resell value is very high for weed...mmmmm] You're telling me. $20 a twomp? Fucking outrageous.
2000 January 13, "BilG4", “Re: How long does a $20 sack last you?”, in rec.drugs.cannabis[4] (Usenet):
HAHAHAHAHAHA i [sic] get at leat [sic] 6 grams in a twomp[…]
