I usually save it for the next day, or sometimes my husband will eat it. I usually make (or order in a restaurant/take out) something that I plan to get 2-3 meals out of. Sometimes by meal #3, I'm just not in the mood for it, and at that point I might toss it. Recent example was a power bowl from Taco Bell. I had it for dinner, then the next day for lunch, then it sat in the fridge for a couple more days til I tossed it!
A common example for me is breakfast sandwiches. I always make one, cut it in half, and wrap up the 2nd half for the following day. Also with salads, I never put dressing on them, and instead dip my fork in the dressing as I eat. Undressed salads keep in the fridge better.