I love the plastic Peanut butter jars-They have a wide mouth, they come in custom sizes (I buy the sizes I need) and they can be frozen! I use these to store and mix salad dressing, to store and mix just a cup or two of powdered milk, as freezable storage for Stock (pre-measured) , to hold small home school items, craft supplies, and more. They fit just right inside of DH's lunch box I add a microwavable bowl and spoon and send his soup in a jar. They are great for road trips and picnics. Store water and freeze overnight to have a sealable glass of drinking water. I have stored leftover tea and coffee for cold coffee drinks. Leftover pancake and waffle mix and can be pored strait from the jar. I usually have 6-8 jars at hand all the time and can easily replace as needed! I could go on but you get the idea.
Be sure to see Shannon's site for more great ideas!