If I can pick up the keg with my pinky, I know there's barely a pint left.
perhaps maybe a fishing scale so you don't have to move the whole thing, just lift, read, subtract the tare weight, and yer done?
Primary: English Mild
On tap: Pale Ale, Lancelot's Wheat, English Brown Ale, Steam Beer, HoovNuts IPA
Bottled: MOAM, Braggot, Raspberry Melomel, Merlot, Apfelwein, Pyment, Sweet mead, Cabernet
Gal in 2009: 27, Gal in 2010: 34, Gal in 2011: 13, Gal in 2012: 10