When we moved from a furnished apartment to an unfurnished one, the list of expenses added up fast: bed, table, chairs, lamps, dressers, etc. One non-essential that was put on the back-burner was a microwave. We just kept saying "we'll budget that in after we get [insert other item here]" or "next month". So, in the meantime, we got creative with our stove and tried different ways of heating up leftovers. We learned that the oven takes forever, and we started opting for the stovetop instead. For most leftovers just stick a pan down, plop your food in, add a splash of water and a lid, and turn the heat up to medium (then reduce it to medium low once the pan has heated up). For liquidy leftovers (such as soups) it's even easier/more obvious—just pour it into a pot, put a lid on to stop splashing, and turn the heat up to medium. Then stir occasionally.
It's kind of funny to think about the superfluous things we have around the house that seem not only normal, but necessary to us. A microwave was one of them for me. Even though I know that people got by for hundreds of years without them, they are a fixed part of a modern home. The stove takes a few minutes longer than the microwave, but, to us, it's worth it. We saved money and precious counter space, and (the best part) we don't end up with rubbery leftovers! It's interesting how necessity gets us to think outside the box (the magic reheat box in this case) and find things we like better. So give it a try just once; forgo your microwave and find out just how much better your leftovers could be. Who knows–you might be converted.