It is imperative that you consult with your IT company to validate that your backups are working properly. This includes trying to restore your data from your backup source(s) and then accessing the data to verify the integrity of it.
Offload all images, data, and business documents, etc. to an external storage device and move to a safe location. Make sure that the data is encrypted. If the file size associated with online backups is substantial, it may take numerous days to restore vs. an external storage solution.
Find and secure all software installation disks so that software can be installed on new computers in the event the PCs need to be replaced.
If you fear flooding, move computers to the highest point in your office (on top of counters, etc.)
Consult with your IT company first, but it may make sense to unplug all your computers and devices to prevent damage due to electrical grid issues.
Have your IT company create a mirror image of all your critical servers and image acquisition computers. This will significantly increase the recovery speed in the event the servers need to be replaced.