Extras are optional non-core rental items that you sell (or rent) alongside your core inventory.

e.g. a helmet, pedals, insurance, lights

Some folks even use it for more 'abstract' things:

mountain ski pass, shuttle ride, cycling jersey, water bottle

They can now be at the Item level or the Reservation Level.

They appear in your online booking alongside your rental items.

Please note that this example shows Item Level Extras.  

For Reservation Level Extras, please consult this article.

Plus they appear in your back office:

You can charge for them or they can be free.

You decide which extras apply to which type of bike.

Please Note:

-  extras do not count towards your inventory count (BRM subscription)

-  however extras do not track your inventory - so you need to have 'an unlimited supply'

See Also

setting up extras 

Setting up Reservation Level Extras

your extras compatibility matrix - which products can have which extras