Connect any 2 regular mouth Mason jars - mix and match any sizes. Widely available in 4oz, 8oz, 12oz, 16oz, and 32oz. Think carefully when you open it so you don't unscrew the jar that is upside down :)

The possibilities are endless:
Quart of salad + 4oz dressing.
Quart of water + 4oz of mixed nuts.
Pint jar half full of yogurt + 4oz or 8oz of granola.
Half pint of carrot sticks + 4oz ranch or hummus.
Quart of soup + whatever toppings you like - croutons, cheese, nuts, scallions, herbs.
Half pint of goldfish crackers + 4oz of raisins.
Half pint of crackers + half pint of juice.

Made of polypropylene, which is a BPA free plastic. Included silicone seals are FDA food grade, or upgrade with 2 full liners that cover the entire inner surface (they don't fit perfectly, but well enough to be leak proof).