Eighner had several experiences while Diving for food. One of those was learning how to tell what was safe to eat and what wasn't. He informed us that, "eating from a dumpster is what separates the dilettanti from the professionals." Things required to be used while Dumpster Diving are the senses, common sense to evaluate the condition of the found materials, knowing the Dumpsters of a given area and checking them regularly, and always seeking to answer the question, 'Why was this discarded?', before being used or consumed. Cans are among the safest things to eat from as long as they have a slight vacuum and suck air when they are first punctured. Raw fruits and vegetables as long as they have intact skins would also most likely be fine. Candy, especially hard candy, is safe as long as it hasn't attracted ants or other insects. College students can be very wasteful and throw out perfectly good food without much thought. They throw it out because they would be going away for some time and were not sure if it would be ok when they returned from their trip.
If the thing you find is a prepared food, there is additional information needed to tell if is safe to eat. He warned that home leftovers as opposed to surpluses from restaurants are more than likely bad. Such as at the Dumpsters around the apartments of the college students, they