Have snap, crack and crunch written on three index cards.
Number snap card 1 and 2, crackle 3 and 4, and crunch 5 and 6.
Roll a die and when 1 or 2 appears on the die respond to things that snap.
If 3 or 4 appears, respond to crackle.
When 5 or 6 appears respond to things that go crunch.