Not looking for anything grand or big
A lot of the restaurants do " lunch menu" between 12 and 4 pm cost will be 16-25 PLN, two or three courses. So this would be your cheap fuel top up for the day, in the evenings it is back to normal price. Milk bars would be a good option if you are on a tight budget. There are also bars offering " happy hours" you have git to smell out your own holes when you are on the ground.
We have "pie & mash" shops in London, which are similar in many ways, but with a somewhat limited menu
Pie, mash and lots of liquor - yes please.