I think buying canned tomatoes in warehouse stores like Sam's and Costco are some of the best deals in the entire store. However, using the entire can in one cooking session is usually out of the question. Generally, when I open a can of diced tomatoes or tomato sauce I generally seal the remainder up in a freezer bag and tuck it into the depths of the deep freeze, but I've recently found a better way for tomato paste. I found that I have a spring loaded disher that will hold exactly one ounce of tomato paste. (Yeah, I had to use my kitchen scale the first time I did it.) I scooped out an entire gigantic can of tomato paste onto two sheet pans and froze it just like you see it above. Once they're frozen, I seal them up in a freezer bag and pull out perfect 1 ounce portions of tomato paste whenever I need them.
P.S. Small cans of tomato paste equal 6 ounces, and large cans of tomato paste equal 12 ounces.