Some of my favourite things to cook aret he using-it-up ones - you never quite know how they will turn out and you'll only manage to make them that exact way once lol.
One of my favourites is just called 'cheesy vegetables'; I get together all the veg that needs using up and prepare ti. Onions, carrots, potatoes, greens, beans, cauliflower, peppers, leeks - almost anything, even if it's soft and bendy, or you have to strip a few outer layers to use the better bits inside. If I use onions, I tend to fry the first, just to colouring stage - gives more flavour I find.
Cut them all up into good sized chunky bits, trying to keep them roughly the same size (not always easy!), then gently boil or steam them until just done, drain well and turn into an oven dish. Make 1 - 2 pints of cheese sauce, depending on size of dish/amount of veg etc. Melt 1 oz butter, add in 1 tbsp plain flour and cook until honeycombing (this shows the gluten in the flour is expanding, hence the sauce will thicken), then gradually add 1 pint of milk, stirring all the time; leave to thciken, then add in grated cheese - another good opportunity to use up bits and ends of cheese that may be lurking lol Just grate them all and into the pan. Stir until melted, then pour over the veg. It can go into the oven like that, or you could add breadcrumbs as a topping - use up ends/slightly stale bread, grated - add in dried herbs, or smoked paprika etc. Cook in a hot oven until golden and bubbly. Nice served with crusty bread :)