A pack of 40 jumper leads of various colours for prototyping.
Each flexible lead have pins to suit breadboards or PCB headers.
Each group of jumpers are connected to each other and can either be pulled apart in any quantity (from 1-40, of course) or kept whole based on you needs.
These jumper wires can be used for pretty much everything! They work great with breadboards, Arduinos, and really any 0.1″ pitch prototyping board.