2. A 6-pack of anything (compare quad).
Neither usage has anything to do with magic or black art, though the pun is appreciated and occasionally used by hackers.
True story: As a joke, some hackers once offered some surplus ICs for sale to be worn as protective amulets against hostile magic.
The chips were, of course, hex inverters.
3. <character> The hash character, used to introduce hexadecimal constants in some assembly languages.