Use the Purchasable Items and Event Tickets grid in the Event Wizard. Click Add New Item and set the name, description, price and any quantity limit.

Items appear during registration, and can also be bought on their own if you allow it. You can mark an item as required so it is added to every registration.

Add an image if you have one - the same 100k limit and automatic resizing apply as for logos.

If your state requires it, set Sales Tax on the event so tax is calculated on items at checkout.