When I was Sales Manager with Tupperware one of the most popular products was the "Quick Shake" which enabled you to easily mix up eggs for omelettes, produce lump free mixture for custard and pancakes etc.
Now if you have lost yours over the years, the nearest I have found to that magic shaker is from Lock & lock which is a 470ml slim tumbler. with a mixer included. It has a liquid tight lid and can also be used for storage.
Have a look at the website www.locknlock.com for more info. the range of different size and shape containers are available in hardware stores.