You need two things: a can of tuna and a can of sweetcorn. Buy both on special offers and store them in your cupboard. They’ll last a long time and they’ll be there when you need a quick meal. It doesn’t need anything else, tuna and sweetcorn come with their own juices but you can add some lemon juice if you like (and if you have it on hand). Lettuce is optional here, but if you have it, it goes well with the combo.