Cooking. So many people don't even have the bare minimum ability to throw something together from raw ingredients that's vaguely nutritious, palatable, and won't give anyone food poisoning, so of course start there - it's so much cheaper than ready meals and there are plenty of recipes that are fast if time constraints are why you use ready meals. In fact, a trick I've always used is to cook something that serves 4-6 people, divide the extra into tubs, and freeze it. That's a few nights where making dinner is as quick and simple as defrosting something, maybe boiling some rice or pasta to go with. Do this with a half-dozen meals and you can alternate and not have to cook for weeks.

Beyond that though, learning a little more about flavour and technique, how to season a dish like a pro, some more unusual flavour combinations etc. can add real interest to your diet for very little extra effort, time, or cost. A few cheap herbs and spices can cost less than a single portion of what you're cooking and give you enough to enhance months worth of meals.

Cooking yourself a treat is great therapy. Cooking something a bit fancy for someone makes for a cheap yet heartfelt date night. Cooking a meal your family enjoys is really satisfying. Everyone should learn to cook, just a little.