To speak about quantities and types of food, you need the appropriate vocabulary.
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.
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.