A: take the crackers away before more mess can be made, but then have to deal with a tantrum throwing little boy.
B: Allow the mess to continue until he gets bored with it, and then show him how to clean it up and make him help you.
C: Let him do whatever he wants because you're making dinner and he's happy and then leave the crackers on the floor for 3 days, and notice that he occasionally helps himself when he is in the kitchen and bored and figure it will all be gone eventually.
I won't tell you which one I went with. But I bet you can't guess. . .