Теория:

To speak about quantities and types of food, you need the appropriate vocabulary.
  
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Bar - a small block of something solid;

Loaf - bread that has been baked in one large piece so that it can be cut into smaller pieces;

Lump - a piece of a solid substance with no particular shape;

Piece - an amount of something, or a part of something;

Pint - a unit for measuring liquid, equal to 0.568 litres in the UK and 0.473 litres in the US;

Portion - a part of something;

Slice - a flat piece of food that has been cut from a larger piece;

Spoonful - the amount of something which can be held on a spoon;

Barbecue - a party at which you cook food over a fire outdoors;

Buffet - a meal in which dishes of food are arranged on a table and you serve yourself;

Four-course meal - meal consisting of 4 dishes;

Picnic - a meal that you make and take with you somewhere to eat outside;

Snack - a small amount of food that you eat between meals;

TV dinner - a meal that can be bought already prepared from a shop and just needs to be heated before being eaten, especially while watching television.
 
Examples:

We're going to have a picnic down by the lake.

Do you want a quick snack before you go out?

A lot of people prefer TV dinner.

She wants a slice of cake.
Источники:
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