You won't use leftovers if you don't see them in the fridge. The best way to know at a glance what's there is put leftovers in a container with a piece of plastic wrap on top and secured with a rubber band which keeps the food airtight and usable for a longer time. Then plan your meal so that these "plannedovers" are used. Stretches your food dollar, a large expenditure in our budget.
Also, to save room in the fridge buy a package of gallon-size plastic bags (the kind secured with a twist tie, not zip lock type, which are much more expensive and don't seal as well as the twist tie). Use these to store leftover tossed salad, rice, fruit, veggies. You'll find all sorts of uses for fridge storage with these bags.