no alcohol or drugs: I quit drinking a year ago. I've saved a LOT of money. In my case, it was a crutch.
Food-wise, I eat very little meat. If I do, I eat pork liver, chicken hearts/gizzards. Offal basically.
Fish can be cheap if you buy it flash frozen or canned.
Peanut butter, bananas, and grapes are cheap.
Instead of bread, I make my own flat bread.
Not OP but tilapia and barramundi are pretty widely available and are generally sustainably farmed and vegetable fed so are cheaper than wild caught or carnivorous fish like salmon.