If you need to do marketably food-safe items, you're best off using your printed part to create a mold for pouring food-safe epoxy. Or at least that's quicker than having to test every print to make sure they haven't acquired contaminants inside the printer, like lead from a Chinese-made brass nozzle.

If you're not intending to sell the printed parts or any food created using them, the main thing you have to account for is the porosity of printed surfaces. There are mutiple ways of dealing with this issue: coat the printed objects, line them with something food-safe, or vapour-smoothe them.

There are filaments available that are certified as food-safe provided the printer is—here's one—but any good quality PLA (and I would expect also PVB and HIPS, since those plastics are used in food packaging—maybe others as well) shouldn't shed anything particularly dangerous. I've never heard of food-safe resin, but that doesn't guarantee that it isn't out there somewhere—I've never owned a resin printer.

The metal-impregnated PLA filaments are mostly "for the looks", but there are some that can probably be detected by various sensors ( here's one that's magnetic )—just be aware that they may not be any stronger than the binding plastic. You might be able to get actual metal parts out of an industrial laser sintering printer (a technology that uses a laser to melt powder), but those are priced way out of the range of a home hobbyist, so I don't know if anyone here has direct experience with them.