A collection of things used for a certain purpose is a kit, like a first aid kit with bandages and aspirin, or a tool kit with hammers, screwdrivers, and wrenches.
There are kits meant for camping, taking care of your cat, and painting landscapes. A group of items needed to build or assemble something is also a kit, like a model airplane kit. The case you keep these things in can also be called a kit. A completely different sort of kit is a baby animal like a fox or beaver kit. A set of drums — bass, tom, snare and cymbals — is commonly called a "drum kit."