Very few. Your best bet is to pack a picnic for the plane. (If you prefer to put condiments on sandwiches or salads just before eating, remember to carry the condiment packets through security in your 3-1-1 baggie. If you pre-spread your bread or pre-dress your salad it isn't an issue.)
In consideration of other passengers, it is best to try to avoid bringing on the following: peanut butter products, "smelly" foods such as tuna or bleu cheese, or things that have bones/skin that must be disposed of (because the odor tends to linger after the meal is consumed.) If you need to keep the food chilled, the best option is to either bag some ice airside to put in with it, or freeze a bag of grapes or peas as a coolant pack.