Since their inception, in the form of the Blunderbuss, shotguns have been loaded with bizarre objects. When lead shot was running low it was not uncommon for a blunderbuss operators to stuff rocks, wood or scrap metal down the barrel to use as expedient projectiles. Tao Fledermaus loaded all sorts of household items, from M&Ms to computer screws, into shotgun shells and videoed the results …
I don’t recommend loading random objects into shotgun shells, unless you are an experienced reloader.
Putting hard metal down your barrel is going to do damage and ruin accuracy/shot spread. While modern shotguns can fire steel shot, remember that steel shot is made form a soft grade of steel and are usually contained inside a plastic cup.
Food, dirt and other mixtures are also a bad idea. They could contain substances that cause or promote oxidization (rust) and these substances could get trapped in small scratches, pitting or the choke threading.
[ Many thanks to Sven (Defence and Freedom) for emailing me the the info. ]