A death kit is an ensemble of tools/weapons used for (or put together in preparation of) a murder. It usually consists of duct tape/rope, knives, a gun, garbage bags etc...
In the case or real killers a death kit will consist more of:
A beautiful array of knives (scalpels, machetes, etc...),
Saran wrap and duct tape (like in the show Dexter),
Garbage Bags (for disposal of body),
Hacksaw (for dismembering the corpse),
Death kits can include any number of many kinds of tools, depending on the situation and what is needed for the murder.
J:Shit man, you've got a dope death kit
L: I know I just put it together yesterday
J: Should you really be showing this around man?
L: Nah, it's cool, this is a special occasion
J: What's the occ------