As long as it's not liquid, they don't care. You can carry a peanut butter sandwich on, but not a jar of peanut butter. You can carry a meat sandwich on, but the mustard must either be on the sandwich or in one of those little condiment foil containers and in your 3-1-1 bag. You can carry bagels with cream cheese on them, but if carried separate, the cream cheese would have to be in a tub less than 3.4 oz and inside your 3-1-1 bag. Fruit of any kind is not problem. Gogurt would be, because it would be considered a liquid. You can not carry drinks through security but can either buy them after security or you can carry an empty water bottle and fill at any fountain after security, then add a drink mix to it. Due to fellow flyers with nut allergies, you might want to avoid anything with nuts. You might also want to avoid anything smelly for the comfort of your fellow passengers.