> Even though I'm pretty frugal, one measure I currently practice is to usually not touch food past the best-by/sell-by/expiration date.

Three different things.

Best-by -> may not be particularly unsafe, but starts tasting gnarly as time goes on.

Sell-by -> the store should sell it by this date, but there's still a healthy margin of time left for you to keep it on your shelves and eat it.

Expiration -> They definitely don't want you to eat it after this date.