You could substitute just about anything for the frozen mixed vegetables. Try sliced carrots, chopped onions, chopped potatoes or whatever.

1 (16 ounce) bag frozen fully cooked meatballs
2 (14 ounce) cans condensed beef broth
1 cup water
2 (14 ounce) cans diced tomatoes with herbs, undrained
1 (16 ounce) bag frozen mixed vegetables

Combine frozen meatballs, broth, water and tomatoes in a 3-4 quart crockpot. Cover and cook on LOW for 9-10 hours or until meatballs are tender when pierced with a fork. Stir in the frozen vegetables and mix well.