A co-worker always brought the best lunches to be microwaved. Leftovers, she explained, that she divided into single servings & placed directly into the freezer rather than constantly facing 'moldy mysteries" a few days later.
Ever since hearing that frugal tip, if we have leftovers that anyone might want to eat at a later date, they go to the freezer, pronto! Has saved me several $$$ on Tupperware and/or Rubbermaid containers over the past couple of years.
The only downside I could see to her way of doing this was that she didn't, as a rule, label her containers & she never knew what she was having for lunch until she microwaved it!