I absolutely live by this free app:

Why Do I Need File Syncing?

Dropbox gives you 2 major benefits: accessing the same files from any device and keeping those files backed up.

Syncing

I can get to the same original source files from my Mac at the office, my Android phone on the road, and my Windows PC at home. Any changes I make to a document on any device syncs back to the Dropbox server and then to each of the other devices.

Backup

Dropbox is better than other backup solutions I’ve looked exactly because of the syncing. More than just keeping a copy of your file on their secure servers, it leaves an offline copy on your device. So when I’m traveling in a plane without internet access, I can work on a file and know that the server will be updated with all of the changes as soon I’m back online.

One planter I worked with had TWO hard drive crashes before launch. He lost precious hours trying to restore lost work and shopping for a new computer. Don’t make yourself an easy target for this kind of spiritual distraction!