A ‣ Containers and contents* 
* the things inside something
Language help
A tin usually has something we eat inside it; a can has something we drink.
B ‣ Quantities* 
Just a drop of milk [a very small amount] and no sugar in my coffee, please.
I’ve cut three slices of beef; that should be enough for the sandwiches. (Or three pieces of beef)
I took my boss a bunch of flowers when I visited her in hospital.
I need a sheet of paper. (Or a piece/bit of paper)
Andrew bought two pairs of trousers and a pair of shoes yesterday.
I bought a couple of books. [two, perhaps three]
We saw several churches on our way here. [some but not a lot, e.g. between three and eight]
I bought half a dozen eggs at the supermarket. [six]
There are a dozen students in the class. [twelve]
Could I have a spoonful of sugar in my tea?
We’ve got plenty of time. [a lot of]
The company is now making the toys in large quantities.
* the amount or number of something
Language help
We can usually use slice when talking about pieces of bread, cakes and meat. We can use bunch to talk about flowers, grapes, bananas and keys.