At a minimum you'll need the System State and the Exchange Server (either via Exchange Agent or a flat file). For the other stuff, C-drive and so on, I would say that it is depending on what your DR plan is.
How to you plan to restore a server in the case of a disaster? Reinstall it from scratch and install exchange and restore the data or use the Disaster Recovery agent from Arcserve?
I hope you find this post helpful.
Regards,
GSC