Many events like to offer additional purchases to those registering to their events and you can too!
Simply add items to your event store when creating the event registration; adding at least one item creates the store page which all registrants will then pass through during their registration flow.
You may add additional items after your event has been published but you will need to communicate with and encourage those already registered to revisit your event page and purchase any new store items they may have missed.
By default your event store will open when your event is published and will close when your event closes, unless you request otherwise by contacting our Help Center (up until the date of the event itself).