Hi Jaap,
Using the additional fields, there is not currently a way (out of the box) to add additional fees based on the user’s selections. However, you should be able to use some WooCommerce extensions to allow users to select these additional products and charge them additional fees. These options will not appear on the event page tickets section, but you can use the full WooCommerce product page for tickets, which will display the options just as a traditional WooCommerce product would. Integrating a third-party plugin with the default tickets form would require a customization – our themer’s guide is the place to start if you would like to give this a shot.
We are limited in the amount of support that we can provide for customizations, but if you get stuck or have any questions, please let me know – I’ll be happy to point you in the right direction!
Thanks,
Jennifer