Have a Disaster Recovery Plan which you review annually. Define who is responsible for what. It should be electronic and in the cloud as well as in paper. Several trusted members of the firm should also keep a paper copy at home.
Communications are always the #1 problem. An emergency contact list should be in paper and in the cloud where it can be accessed via a computer or a phone.
In case of flooding or mass destruction, it is best to have a backup in the cloud. Test your backup regularly to make sure it is working. There are many reputable cloud providers – examples include Mozy, Carbonite, Backblaze, CrashPlan SMB and Acronis.