In order to backup all important business data, I recommend a redundant system of external hard drives. Not only will these protect your files in case of catastrophic computer failure, but they offer an extension on your hard drive storage space. These drives are quite reasonably priced and typically plug directly into the extra USB ports on the computer.
They are compatible with a desktop and laptop to protect all of your files and are small enough to be portable should you decide to bring them on a business trip. The specific model I recommend is the Western Digital “My Passport” with two terabytes of storage space at just $139.
In addition to these external drives, you will also want to add a selection of important documents to the cloud using Dropbox. This service allows you to access uploaded files from any computer with internet access, and also has a mobile app for the phone. You can share documents with clients this way, or just use it for extra protection in case all of your hard drives were damaged or stolen. It is quite secure with 256-bit AES encryption and two-step verification & mobile passcodes. This cloud service is reasonably priced at $99 per year for 100GB of online storage.