Invention Idea - Top and Bottom Interlocking Building Block Crockery/ Also: Domestic Usherette Tray/Usherette Box

Recently i had to take a cup of tea up to my elderly father and my sister aswell as a slice of cake. I didn't know how I was going to carry them all upstairs but then I thought that, if I put the cake into the upside down lid of an old coffee jar, it will fit nicely ontop of one of the mugs, then I can take it upstairs and I wont drop it.
And that is how I thought of the idea of having crockery where the bottom of every piece of crockery is designed to fit neatly like a building block into the top of another piece of crockery so that you can carry cups stacked upon each other or bowls ontop of cups without them falling down. It helps if the bowls are not much larger than the cups too because that will make them easier to balance.
Furthermore, I think this type of crockery would be a useful aid in the catering industry for waiters having to carry lots cups of coffee and cakes
Note: After searching on Google I have found crockery that interlocks at the side but I think that this is less efficient than my top and bottom interlocking idea. With top and bottom interlocking you could probably carry atleast 6 pieces of crockery if you held 3 stacked pieces in either hand.

Usherette tray for domestic use/Also: Usherette box
You know those trays that usherettes use in the theater and cinema for serving snacks during the intermission with a strap that goes round your neck? Well, why not have them for domestic use so that you can carry cups and plates and other items of crockery and cutlery about your house. Futhermore, you could have boxes like this to help you carry slightly heavier items short distances because, with a strap to fit around your neck it would mean that the weight of the box was distributed between your hands/arms and your neck.