...it's not a good idea to cook in plastic, not even in the microwave. Even if you don't ruin the plastic, you could ruin the food. Many plastics shouldn't be in contact with hot food, even if they'll survive a trip in the microwave. Stuff in some plastics leaches out. Sometimes you can even taste it, but even if you can't, it's no good for you.

If you're going to put food in a microwave, transfer it to a microwave-safe plate, bowl or dish first. If you need to cover it, use another dish or bowl. Do not use plastic dishes or anything metal, not even a little.

For a traditional oven, only use cookware that belongs in a conventional oven, like a baking pan, aluminum disposables, or heat-proof glass. If you need a cover and don't have one, use foil.

You can also reheat things like stews on the stove. Put a little (like 1/4") water in a pot, bring to a simmer, then add food, cover, and reduce heat. Watch like a hawk and don't let all the liquid boil off. When the lid is too hot to touch, stir the food and re-cover for a few more minutes, repeat as necessary.

I understand the difficulty some people have in the kitchen, but I've always been pretty comfortable around it. It's a shame they don't teach basic food prep in high school to everyone. It's a useful thing, and would be good to at least demystify.

Personally, I'm not big on leftovers or prepared foods, and I try to avoid them. Even simple things, cooked fresh, seem better to me.