TRYTN allows you to not only sell additional add-ons to make your experiences more memorable, but also to add required items or fees to your products. In order to make an add-on be required for purchase navigate to the product type and either create or edit a product. On the Advanced Settings screen you will find a section for add-ons. Select at least one add on. If you do not have any add-ons in this section you will need to create at least one add on.
Once you have selected at least one add-on for your product you will see the above screen. Check the Check this box to require this add-on to be purchased checkbox. Any customer that adds this product to their cart will also be notified that they also must purchase this add-on and their totals will reflect this item.