Recommended for pigs is formulated pig food, which looks like big pellets. The kind I feed my pig is "Lab Animal Mini-Pig Food," which I bought from a store called "Southern States." Purina also makes a formulated food for pot-bellied pigs.

Do not feed your pig normal farm pig food. This food is designed to fatten a pig for slaughter, and will make piggy fat.

Do not feed table scraps to your pig. This will make him exceedingly fat. The vet told me that some pigs are fed so much, their small legs can no longer support their bodies and the pig has to be put to sleep. :(
You can, however, use vegetables and fruit as treats for the pig when it has done something good (pottied in her litter box, followed through with a command ("sit"), etc.) but do not over-indulge the pig. Dixie likes oranges, tangerines, banana, apples, broccoli, water chestnuts, and peas. She does not like (even I was surprised that there is something she will not eat) carrots.

The vet told me to feed Dixie 3% of her body weight each day. At 8 weeks and 13 lbs., this meant that Dixie would receive 6 oz. weight (not volume) of food daily. Now, at 3 mos. and 18 lbs., she gets about 8 oz. of food daily.

As a side note, if you want to teach your pig a trick or if you just want to bribe it into doing something (going outside when it doesn't want to), use food, and you are guaranteed success.