Depends on what you're cooking and what method. In general, stainless steel, anodized aluminum, and enameled cast iron are safe choices. Of course they have their drawbacks for some cooking...
I have taken fresh kielbasa (or bratwurst) and sauerkraut and after the kielbasa was cooked, I added frozen perogies, nestling them in the sauerkraut, and cooked another hour..came out great