Rice and beans can be cooked up all kinds of different ways with a variety of spices/salsas/etc. It's also versatile, you can add chopped peppers, corn, tomatoes, or whatever veggies you have to make a rice bowl or buy tortillas and use as a base for burrito filling.
Buy a rotisserie chicken once a week and use the shredded chicken for quesadillas, chicken salad sandwiches, protein for salads, pasta, etc.
Big batches of hard boiled eggs make great grab and go snacks.
Stir fries with whatever meat and veggies are on sale, and it's really easy to make a homemade sauce (I use 1/3 cup soy sauce, 1/4 cup brown sugar, tsp-ish of ginger, 2 cloves of garlic and tsp-ish of sesame oil). Mushrooms, peppers, broccoli, onions, carrots, green beans, onions - whatever is lowest cost that week!
Keep stables like chick peas and cans of tuna around. For a super quick lunch or dinner, dump a can of tuna in olive oil and a can of chick peas together, add a touch of balsamic vinegar and whatever leftover veggies you have in the fridge.
In the fall/winter, a big pot of chili (veggie, ground beef or chicken) is awesome and can be stretched even further over rice. This is my favourite chili recipe:
http://iowagirleats.com/2014/09/24/signature-spicy-smoky-sweet-chili-crock-pot-friendly/
I think one of the most important things is a good spice set, good spices can really make even the most inexpensive food tasty if you know how to season it well!