As an aside, this is one of the reasons that those fallout or radiation suits that you see in all the pictures and movies and on TV are such a joke. Those things are not going to protect the guy from anything, that a couple of good garbage bags wrapped around his feet and made into a hood to go over his head, would not do as well. In fact the garbage bags are in many ways better. They would be considered disposable.
The main purpose of the fallout suits is to prevent the wearer from tracking the fallout into the shelter. The user simply takes the suit off at the door. If the person were to wear it on inside, it would defeat the purpose. There are some clean handling techniques that are beneficial to know and practice, but in a wartime situation there is so much of the stuff around that peacetime standards of exposure and cleanliness lose their meaning.
The gamma rays are another matter. They are very penetrating. No fallout or radiation suit is going to protect you from them. It requires much more dense matter to protect you than you could lift, let alone lug around. This is why one must remain in a shelter when there is intense radiation. With good housekeeping there should not be so much dust inside a shelter as to create a hazard from gamma rays. However, be sure to dispose of the contaminated rinse water that you have used for cleaning the food containers and persons returning from outside. It may contain matter that is giving off gamma rays.
There will probably not be sufficient fallout on the food packages (or you can get rid of it quickly enough) that you need concern yourself about the amount of gamma radiation that you are going to get from that source during the decontamination process. However, the food may have been stored in an area that has received very intense radiation. That can of beans or peaches may have been stored right out there where it was receiving 1000 roentgens of radiation per hour. An amount that would have killed you right away. But it will not be harmed.
That is right. It is perfectly edible. If it were not so I would have told you. It is only living things that radiation hurts. Even then it depends upon the frequency and intensity of the radiation. For example, there are all sorts of radio and TV waves going right through where you are sitting right now and they are not harming you.
The food in the can is already dead and the gamma rays are not going to harm it. They will not make it radioactive. If the radiation is strong enough it may kill any bacteria that happen to still be living in the food and thus preserve it even further. If the food is supposed to contain bacteria (such as yogurt) I am not sure what it would do for that!
Radiation preservation of food is a technique that is already being used in industry and will probably become much more widely used in future years. Many people already have radiation (microwave) ovens in their homes today. One further analogy. Fire will kill living animals but we use it to cook our food. You really shouldn't be overly frightened about radiation, either.