Remembering users v/ cookies

I want to have a option on my site that users can check a checkbox that says “Remember me” and if the users checks it beforloging onto the Site I would register a cookie with some values about the user, but I’m conserned about how I should store the info in the cookie. I want to keep track of the userId, usserName, but I would’t want to keep is passwd int the cookie would I? any sugestions on how to make this so that not any idiot can break into it? Regards, David