if they have enough fridge and freezer space < this is a big issue. There is no point batch cooking when you only have half a freezer drawer.
My DC were pretty competent cooks before they went to uni but we did a run through of cooking for one and meal planning so spare ingredients and leftovers don't go to waste, for example:
Mix a standard 400g packet of mince and a large chopped onion, take a quarter to mix with herbs and breadcrumbs to make bifteki (or a burger), add garlic puree and cook the rest, take a quarter and turn into cottage pie, add a tin of chopped tomatoes then split into 2, add herbs to one portion when you reheat it to make spaghetti bolognese, add beans and chilli powder to make chilli.
Similarly, we did the whole Mumsnet roast chicken thing:
Sunday roast/chicken Caesar salad/Thai and Indian curries/stir fry/chicken & mushroom pie/chicken fried rice/chicken soup etc Obviously not all from the same chicken!
A packet of sausages made into sausage and mash/cassoulet/toad in the hole.
We also did variations on basic tomato and cheese sauces to make multiple different dishes, a simple vegetable soup base where you can substitute the main ingredient (if you can make tomato soup, you can make butternut squash or Jerusalem artichoke soup), the basis for different casseroles ie how to brown meat, which vegetables need precooking or adding at the last minute.