I like to claim that I am a culinary surgeon who brings dead food back to life. Professionally and at home, nothing gets tossed out.
The most essential item for me as a leftover, is rice. With that I can make all sorts of things.
Plain white rice is great for burritos and fried rice. I love fried rice as I use many vegetables and whatever leftover meat needs to be moved. The burritos will use whatever meat was cooked before.
I will also make food just for post-midnight snack. That is very important.