I use either wide fabric, pieced one fabric (say 5 yards of one fabric), or horrors - a sheet...
I had a woman say to me, "The back should be as good as the front - think about it, what gets the most WEAR - the front or back?".... she's right, the back is what gets the most wear...
I try to co-ordinate the front and back with regard to color and if I use a floral print (or other print) it 'goes with' what's on front - I don't want anything jarring, or incongruous... or slapdash...