I don't use many convenience foods in meal preparation. I used to rely on canned soups (mushroom, whatever) for casseroles until I learned to make the equivalent from scratch. (Lower sodium and no preservatives!!) Here's my recipe:
Condensed Cream of Whatever Soup
4 TBSP flour
4 TBSP oil (or butter or shortening)
1.25 cups liquid
salt and pepper to taste
Mix oil & flour in small saucepan. Heat until simmering, then slowly stir in the liquid and cook until thickened. Add salt and pepper -- and additional seasonings as desired.
For cream of chicken soup, just use 1/2 chicken stock and 1/2 milk. You can make it creamier by using all chicken stock into which you've dissolved 1/2 cup of dried milk. For cream of celery, saute chopped celery with the flour & oil mixture. For mushroom soup, saute mushrooms with flour & oil and if you are using canned/jar mushrooms, use the juice from the jar and add milk to make the 1.25 cups. For tomato soup, use tomato juice for your liquid & season with celery salt or basil. For cheese soup, add 1 cup of shredded cheese.
This makes the equivalent of a 10-ounce can of condensed soup.