OH! I've been living dangerously and disgustingly for years, it seems
We keep all bones in the freezer and make stock that then gets used for gravy or soup, again kept in the freezer. As OP said you use old veg, cooked leftovers and anything to add flavour. So you use up all sorts of things that would go to waste.
If you put the finished warm stock in a jug in the fridge for half an hour the fat solidifies and you can pick it up as a solid disk, easy to put in the food caddy.
When we have it as soup it again uses up leftovers, bits of cooked chicken, odd bits if vegetables, chopped small, etc. So you get a second chance to reduce food waste.
We did much the same with soft tomatoes and peppers too. Keep all bits, cooked or raw in a bag in the freezer until you have enough then cook it down and freeze back the soup. Eat that with soda bread just out if the oven, or push the boat out and make a cheesy bread... we freeze heels of cheese for bread and sauces too.
I know that sounds OTT to many, but it is easy enough to have 3 large bags, freezer or carrier bags, permanently in the freezer ready for bits and bobs to be made into all sorts of meals later. Once you have 2 or 3 recipes for each bag you start to plan for it, reducing food waste even further.
That and it's fun trying to work out whether the food you are about to drop into the bin could have a second shot at hitting your plate instead.