How to remember the selected foo before and after a registration process?
I tried a lot of things with logintoboggan but the unauthenticaed role makes it diffecult for other modules to make well. So if you try to establish this with logintoboggan you are implicied chosing for modules which are only compatible with the adjustment of the login system. Something I do not prefer. 

I solved it with the following modules:

Email_registration          fo the username is not needed anymore
GenPas                      for generating a auto password and direct login     
Persistent login            for login in for a long time
User email verification     for verify the email 
nocurrent_pass              for remove password edit’s profile  
email_confirm               when user changes email  


When a anonymous gets on the site reqistrating is posssible with only email. With a rule you give the person a role. After that you can do what you like. If the person does not have a role yet and clicks on the link for premium content, you just append the unique id to the registration url and after registration a redirect can pick this up, the person is then verified with a first pre member role.

You send all pre member roles an email with user email verification. If this is verified u can use a rule to upgrade the role. You now have a full registrated process without have the disadvanced of logintobboggan concept and in line with tha fact that no passwords are send by email.