Talking About A Limited Quantity Of Something

To talk about a limited quantity of something we often use the word piece or bit, together with of, before an uncountable noun. Note that bit is informal and usually suggests a small quantity.

The most common expressions of this kind are:

A piece / bit of cake / bread
A piece / bit of paper / wood
A piece / bit of news / information
A piece of advice
A piece of spaghetti
A piece of furniture
A piece of luggage

Other words like bar, blade, drop etc are also used. But note that they are less general and are used before particular nouns. Some common examples are:

A bar of chocolate / soap
A blade of grass
A block of ice
A drop of water /oil
A grain of salt / rice / sand / corn
An item of clothing / furniture
A loaf of bread
A slice of bread / cake / meat
A lump of sugar / coal
A speck of dust
A sheet of paper / metal / plastic / stamps
A stick of chalk
A strip of land / water
A suit of clothes

Pairs

Pair is used for many things that normally come in pairs. Examples are:

A pair of shoes / socks / ear-rings
A pair of glasses / binoculars
A pair of trousers / jeans
A pair of scissors / pliers