Hi, Paula.
Thanks for your interest in our products.
Event Tickets Plus (ET+) has functionality to accept custom information per ticket with the Attendee Meta Information feature. You could offer T-shirt size, for example.
However, it does not have the ability to change the price of the ticket or add additional items to the cart.
I believe you’re requesting the same thing as one of our existing feature requests:
Please do add your vote if one applies to your question. This allows us to gauge interest in this particular feature request, which helps us prioritize our development efforts.
Last but not least, we have a pretty great Refund Policy so you can buy one or many of our add-ons and thoroughly test them.
I hope this info helps. Let me know if you have any follow-up questions.