= Let the kids color on them, then send them through a paper shredder to make confetti.
= Grind them up in a food processor or blender with water to make a mush. Spread the mush on a screen & let dry to make your own recycled paper/greeting cardstock (depending on how thick you make it).
= Use them for fire starters.
= For future readers, if the cards are blank on one side, use them for as "slips" for free drawings / raffles.
= Make flash cards. Paint with tempura or other paint; let dry. Put ABC's, numbers, times tables (for kids) or (for you) muscles; origins, insertions, actions, innervations; acupressure meridians & points. You could also make a "Concentration" or "Go Fish" game after the paint is dry.
= Use as a "guessing game" at a kids' carnival or similar event. Use clear 2" wide tape to create a block of them. Be sure to count them before you tape the block together, lol!
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= Donate them to an elementary school arts & crafts teacher or mixed-medium artist.
= Grind them up (as in the first two above) and mix into a compost or use for mulch.
= Soak them and use for paper machรฉ or to make a piรฑata.