Only two of us - me and my 6'2" lump of a husband so we cook like this all the time. We do similar things, but also here are a few suggestions if you don't already to.
Aubergine bake
Its a vege option but it doesn't really feel like it as it is filling. Dead easy to make too. It can be added to as you wish with the odd extra ingredient to your taste - think mediterranean (onions, garlic, peppers, chillis, etc).
Not got exact quantities - it really depends on how big the dish you are using is. Layer thin slices of aubergine with tinned tomatoes. Go heavy on the tomatoes - you only need one/two layers of aubergine. You can put a layer of courgette in too if you wish. Drizzle a bit of balsamic over the top for extra flavour. Add herbs too in this way if you want (not necessary but it does help the taste). Put a thin layer of grated cheese on top and then cover with a layer of breadcrumbs.
Whack in the oven until top is golden brown and cooked throughout (bout 30mins but depends on size of the dish you used). You don't need to serve it with anything really as everything is in it, but salad or garlic bread is nice.
Pasta bake
Similar to the above but with pasta (tubes or spirals - no need to cook first - just make such decent amount of moisture in the mix.) instead of aubergine (though you can do with aubergine if you choose). You can throw in a small amount of meat too if you wish - you really don't need much as it is filling. Much easier than a lasagne to make.
Have you thought about 'jazzing up your casseroles' by turning them into pies? (or even a wellington - wrap meat and veg up in puff pastry). Generally means you don't need to serve anything on the side again as you have your carbs in the pastry.
If you are doing stews, I'd highly recommend using celery as a base. Finely chop up 3 or 4 sticks with one onion and fry up until onions are just browning. THEN add rest of your veg and meat. It adds a lot to the flavour and is v healthy. Pearl barley in stews is amazing - cheap and makes it go loads further.
How about something like a noodle broth - basically veg/meat in stock. Boil it up and let it reduce a little. Add noodles. You can do a chicken and sweetcorn broth (add chilli and ginger for extra zing). Or a beef version with cheap cut of beef, add a bunch of frozen veg straight from the bag.
We've done sweet potatoes for shepards pie and it works a treat. Sweet potatoes also make amazing wedges if you spice/season them up. If you do curries, sweet potato is brilliant to bulk it out, without loosing flavour and it makes it go further.
I like adding something like split peas as an alternative to beans. They aren't to everyones taste though. They are nuttier in flavour. Or lentils instead of meat.
We quite often will do a roast chicken on a weekend when we have a bit of time. Much cheaper than buying breasts or other cuts if you are smart about how you do it. We have to make it last to make it worthwhile. We like to do extra veg - butternut squash, peppers and onions are nice for a roast veg soup, but it can be anything - we then use the stock from the chicken and left over veg for soup. Rule of thumb is, if veg work together well on your plate then if you through in a pan and blend they make a great soup! No need to add anything else.
Whatever chicken we don't eat we either freeze in portion sizes amounts and deep freeze morning we eat or use in next couple of days with other things. Stir fries are easy to do with frozen veg, roast chicken and rice. Or you can use the chicken with tinned tomatoes, chopped onion, veg and pasta.