An 'emergency' yo-yo that is completely 3D printed (2 sides and an axle) and uses pocket change to completely assemble (a bill and quarter for the axle, and up to 12 dimes for weight)

Dimes slide into each side to add centrifugal force, it is too light without them. The bill is folded up and creates the structure for the axle, and holds the two sides together with the quarter like a wing nut.
The project includes instructions, which are slightly tongue in cheek and meant to be a little confusing like an emergency first aid kit's instructions.

Each side can also be made into a spinning top, using a bill and one dime.

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