You might want to look into a hosted BES solution like ExchangeMyMail or Link2Exchange. Both are listed in our sponsor are of the forum. I don't know of any third-party solutions for BIS to give you folders.
I use the Saved Items folder for exactly the kind of things you're looking to save. Hotel confirms, flight info, emails with info I want to reference, etc.
I've just begun using WorldMate Live
for my travel arrangements. It's expensive, but it's the class of the travel app genre.