One of my dogs ate a cube of butter in the tin foil wrapping.

I gave them each 4 slices of rice bread to help pass it.

Should I give them some canned pumpkin also?

Skip the pumpkin. My dogs have eaten all sorts of stuff and they were just fine and dandy. One of my German Shepards ate a frozen steak, baggie and all and was just fine. My Jack Russell has eaten all sorts of strange stuff and she was just fine also. You might want to do a little investigation in the yard when they go #2 tomorrow morning and see what develops. If you feel that the tin foil has not come out, then take to the vets for further spelunking adventures. My Jack loves QTips and thinks they are dessert. No ill effects from QTips (the ones with paper sticks).

Keep an eye on your dog, he should be fine. If he's vommitting or has the runs, won't eat or drink, then you may want to call the vet, tell him the circumstances and see if he wants you to bring him in.