You can specify additional information that you want to capture about each of your customers.  

You can also specify which fields are visible and mandatory across your various channels.

You do that by entering in Custom Fields in system Settings > CustomerData:

Here is how the page looks when you access it:

If you want to ask the question per item (e.g. for each bike in a multi-bike booking) then ensure you set the scope to 'per item'.

In the above example you can see that we already show the default fields.  

If you add Custom fields they are shown in blue writing and can be deleted.

This example shows Drivers license on the self registration form:

Finally, in the back-office you can see the new fields, as they were made visible to the back-end using the checkboxes:

changing the order of your fields

if you want to change the order of your customer fields please just drag and drop them into your desired order:

See Also

capturing per rider information

capturing customer data in your online booking (legacy)

customizing the customer data by product