Gruel! Three spoons of oatmeal in a bowl, pour about 500ml (~1 pint) of boiling water on it. You can put a bit more oatmeal in, but if you go too far you get porridge. You're aiming for thin or miserly porridge.

For a mild seasoning, you can cry over the bowl, and let the salt from your tears enhance the subtle flavours. If you're feeling rich, salt can be purchased from shops and used instead.

For optional nutrients beyond simple survival, you can then throw any leftover or past-best veg, precooked meat or edible garden plants in the bowl. For deliciousness, you can add a bit of butter, or even cheese.

Heat it in a pan on the hob, whilst stirring, for as long as you can be bothered waiting. Cooking for longer tends to make it taste better. Alternately, microwave it for a few minutes.

You're ultimately going to end up with something like a thick soup (or a luxurious cheese sauce, depending on ingredients) that's surprisingly filling, and significantly nicer tasting than you might expect from the description.

Gruel. It sounds shit, but it's ace.