There’s a variety of lunches that are cheap and insanely easy though:
Stir fry with leftover rice, an egg, and some frozen veggies
Sandwich with a piece of fruit or some veggies
Leftover soup heated up on the stove (or in the microwave if ya nasty)
Cold pasta dishes like pasta salad with leftover protein thrown on top
Charcuterie plate with cold cuts, crackers, cheeses, and jams
Salad with cold leftover proteins
Leftover fried chicken straight out the fridge, as God intended
Like sure, some of these things rely on having leftovers laying around to dress up a bit, but I think that’s a reasonable thing to expect of most people.