Keeping lots of data from one request to the next -- is flashdata usable for this?

[eluser]mddd[/eluser]
Flash data is put in the user's cookie. It is sent to the user. If it is a lot, it's better to store it on the server.

The easiest way is to use session variables. (Not CI's session, but php's $_SESSION).
You could also store data in the database or in a file and get it back when the user reload, bases on the unique session id that is in the CI session.