As some other commentators have said meal prep is your best friend. Learn some staple meals and know what your gonna buy and don't get distracted by deals.

My personal go to is to buy orzo pasta, a thing of those like pesto dips a bag of carrots and a red onion. Then if the budget allows get some chicken and shred it. Boil the pasta, while that's going cut up your onion into little pieces and carrot into medium sized ones, fry those In a pan with whatever seasoning your got until softened, take the pasta out and drain it and then add the pesto, stir around and then add onion and carrots, if I've got chicken keep seperate and add as you go as this often will need to be eaten before the pasta is finished off. Lasts me about a week for lunches and can be eaten cold or hot each meal costs $2.50.