Survey: session tracking while loggin

Hello,

I want to save user-specific data (like a shopping basket).

Two questions:

(1) how can I identify a not-logged in user ( does wordpress provide a standard session id or another identification for not looged in users)?

(2) how can I assign the logged in user-information (e.g. $current_user->user_login) to the session_id from (1) ?

Thanks for any help!