Exclusively homecooking. I’m not that good at it and a lot of it is deepfrozen pizza, fish sticks, baked fries etc., but even convenience food like that is just so much cheaper than restaurants. If you live with a partner, cooking is even more time-efficient than for one person alone! Meal preparation in advance goes a long way, too, though for me that kinda falls flat because my fridge doesn’t have enough space.

Back when I was in university, I often went to the uni cafeteria, which was a lot cheaper than a restaurant. If your city has one, look into whether it’s open for outsiders - ours had higher prices for non-students, but it was still cheaper than restaurants.