Rice, dry beans, lentils, dried peas, quinoa - for protein
Canned or frozen vegetables - whatever is on sale. And a bag of potatoes.
Fruit - apples are really reasonable right now
Make more soup - do you have a crock pot?
Check out the "clearance" vegetable bin at your grocery store - there you will find the beginnings of more soup/stew - just add beans/rice and seasonings and you are good to go
Here is a thread with some great ideas as well!