I need a shopping cart that will allow me to sell a item based on you are purchasing a primary item first then only allow a secondary item to add to the cart if you already selected the primary one.
For example:
I have a seminar meeting that requires that the person has to purchase the registration, before they can elect the banquet meal or meals. Meaning you can't just attend the banquet unless you are paying for registration also.
I don't want the person to be able to purchase a meal for themselves and family without adding the registration first.
And I don't want the experience to be a two part process to pay for.

I currently tried zencart but it does not seem to meet my needs.
Unless I missed it.

Any ideas?

probably overkill, looked at magento?

Magento is nice, with a strong developer/support community.

Magento can be a pig. I have a site I have been unable to upgrade due to various problems. It has a steep learning curve.

However, you should be able to do what you want with it using shopping cart rules or product bundles. I'd be happy to test this for you since I have a test site installed.

Not sure if any of the Wordpress shopping cart solutions could do this.