What are bar magnets used for?

rectangle bar magnet with iron filings and compasses to highlight magnetic field     

There are many uses of a bar magnet but to illustrate the wide range of uses, here are a few examples:

Bar magnets are used to highlight the magnetic field to children at school using iron filings.

multicoloured letter fridge magnets with labelled rectangle bar magnets     

As fridge magnets

Did you know - A fridge magnet has a magnetic field that is about 20 times stronger than the earth!?
 
Hand placing a bar magnet into a oil filter

    
Bar magnets are used within a car's oil filter to help remove any ferromagnetic materials which could damage the engine. By doing this it makes the engine last longer.
              
HSMAG says "A ferromagnetic material is a term for anything attracted by a magnetic force. To be ferromagnetic it must contain a element of iron, nickel, cobalt, or gadolinium"  
            
Magnetic catch with labelled rectangle bar magnets on a cupboard door

Magnetic catches on doors to hold them shut.

            
Guitar with labelled guitar pickups with a bar magnet inside     

They are used inside pickups in guitars to create different tones. The bar magnet is placed inside the pickup with a length of wire coiled around it to create a magnetic field. Whenever a guitar string vibrates in that magnetic field, the coil detects the changes and then creates a voltage, thus producing a perfect sound.