Once they have been created in your catalog, Fixed Price (Type = Sellable or Signup)* items can be offered for sale during the ticket sales process to ticket buyers and non-ticket buyers.
Items can be flagged to offer during registration at Site Settings > Registration > Tickets > Add-on Items.
Add-on items purchased during ticket sales will display on the Check-in screen for distribution at your event (whether the purchases display for the ticket buyer or their guest(s) depends on where the item is offered on the form.)
*Because virtually all states regulate (or ban) online raffles (gambling), items with type = raffle cannot be offered online. If you are in compliance with your state's regulations, you can offer raffle items as add-on items by editing type = sellable and FMV = price.
To flag add-on items from Ticket Sales settings:
Go to Site Settings > Registration > Tickets > Add-on Items.
Note: Only items that already exist in your catalog can be added.