I will outline the steps that you need to take to create the registry:
1. first you will need to create registry table that includes a product id which will reference your products table, a registry name.
2. you will need to use security assist to create the login and registeration page for your users (you will need to create a users table).
3. once a user logs in, you will need to add an add to registry button which will inserts to your registry table the product id and the name of the registry.
4. then you will need to a search or a login page where the user can enter the registry name.
5. then you will show a product results page (using dataassist) to show all products specific to the registry name.
6. on the results page you can either add an add to cart button or use the add multiple item server behavior from eCart.
finally, i would recommend deleting the products purchased on your checkout success page from the registry table.
The success of the process depends on how comfortable you are with the webassist extensions. In addition, custom coding will have to be added on the product results page and the check out success page.
You can also, look at the Job board to get some help from the community experts.
Let me know if you still have any other questions.