Diced tomatoes can provide a similar flavor to tomato sauce but will also add more liquid to the stew. You may want to drain the tomatoes before adding them to the stew to avoid making it too soupy. Tomato puree is a thicker version of tomato sauce and can be used in place of the tomato sauce. If you don't have any tomato products on hand, you can use red wine or beef broth to add depth of flavor to your beef stew. Just be sure to adjust the amount of liquid in the recipe accordingly.