Hello @SCB21 ,
This is a very open use-case to answer.
From the available list, you can create any type of data element but you need to ensure that this element populates before your ID sync rule fires. The order is key here.
if you are trying to store userid in the cookie then I would say that it is not a good implementation as user details will be available directly in the cookie.
I hope this gives some direction to your use-case.
Regards
Ankita