Can you try to summarize your rules of thumb on consumption of leftovers, and describe to what extent you think they've got a rational basis?

The primary things that come to mind are "if you notice anything off, dispose of it" and "store things in sealed containers with dates on post-it notes or written with dry erase markers," but most of the stuff I pay attention to these days are food prep rules (since I very rarely have leftovers, and most of the things I consume take a long time to go bad).