You can use the session object to store things you need in other places of your web-app. With the many assemblies which make an app it is sometimes a little puzzling where your session objects can be reached and where they are unavailable. When your code enters another assembly (like a classlib) your objects will be there. But when your app enters a page in another webapp (that is another virtual IIS directory) your session objects are unreachable. It does make sense when I start thinking about it (imagine some other alien app fiddling with your session objects..). But it had me pulling my hair for some time. (Yes you may laugh..)
When you want to exchange data with another webapplication you can use a cookie. The bad thing about that is that it takes some more effort to administer those (don't forget to remove), cookies can only store string values and cookies travel over the wire from and to the client. But they do work.
Peter