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One forgotten leftover are the 'heels' from your loaf of bread. You can also include a leftover roll , piece of french bread, etc. I put these in a bag in my freezer and when full, I grind them in my food processor for instant bread crumbs. I can't remember the last time I have actually purchased bread crumbs from the store! I then store the crumbs in air-tight freezer cartons. I have also taken the time to cut them into strips and make croutons by seasoning and toasting in the oven. A side note on the bread bags. I dust out as much as possible and store in my freezer door. I grab these for sharing my summer veggies from my garden. (keeping in the freezer eliminates worry over any little pests)

I almost always make impromptu meals from left over veggies, sauces, rice or whatever is available, mostly the meal turns out quite well. I try not to throw out food. I add veggies, rice, chicken broth, or toasted cut up good bread to my pets meals, they love it.
I warm up can food with additions in the microwave under 10 seconds from the refrigerator. Or heat up broth &/or veggies/rice/potato then put dry food on top, it is not refused.

very good leftover

A good pot of beans will keep you warm inside out, and they are good for you too, throw in any kind of leftover meat and it's really delicious. Another staple that I love beef stew, you use all the leftover veggies and any kind of beef or chicken you choose for a great stew.