Backup to SD card in kit kat
I'm not sure what you're wanting to back up, but most backup applications on the Play Store will do this for you.  Examples are MyBackup Root, Titanium Backup, and Helium.

EDIT:  Scratch that.  As mentioned by Izzy in the comments below, you must be rooted for these apps to work, as there is a..."feature"...in Android 4.4 KitKat that prevents "rouge" SD Card access: link