There are a few excellent free cloud storage providers out there which will sync a directories on your PC or Mac to your portable devices. With Apple Store and Google Play apps to download to access your account you are set for always having access to your home PC files.
Here are three that I would recommend which offer a good amount of storage and more importantly the synchronisation ability across the devices.
Sugarsync
5Gb Free Space. Free sign up.Offers you the ability to share your files between PC, Mac, Android and iOS devices.
Sugarsync
Dropbox
2Gb free space and free sign up.Always have your stuff when you need it with @Dropbox.
Again synchronise your files across all your PCs, Mac, Android and iOS devices.
Dropbox
CX.com
Get a whopping 10Gb of free space to start, and begin synchronising across all your devices.CX.com
All three of these services work in a similar way, and used at the same time can give you a hugh 17Gb of synchronised file space across your devices or for those essential backups.