It isn't only cheaper to cook from scratch, healthier to. Less salt, preservatives and other unpronounceable chemicals.
Ground beef - depending on size you make your hamburgers, you will still have a portion of that pound to freeze and use for another meal later.
Chicken - here at least, a whole chicken costs more then buying parts. example is chicken quarters is around .59 lb, you can occasionally catch chicken breast with bone .99 lb, boneless, skinless 1.99 lb. chick legs or thighs .99 lb. Use what you want of the package, freeze the rest for later.
Experiment with store brands and less known brands - many taste as good or better then the name brands and costs much less.
Bread - visit a bread store. usually about 1/2 the price. You don't use a full loaf of bread - freeze half of it. Need only 1 bun - freeze the remainder.
Just a few ideas..