A:
Anything, if you've caught a fish on it you can probably use it to bait a trap. This includes but is not limited to crackers, bread, chicken liver, hot dog, chum, and various stink baits and scents. Minnows and other small fish are timid you have to let the trap "soak" for a while (depending on the amount of baitfish in the area). and minnows and such tend to feed at night so make sure the trap is in the water when they are feeding.
The trick is to get the first minnow in the trap. Minnows love to school ,instinctively so whenever one gets caught it's a lot easier to convince other minnows to join it.