Wiktionary
pony keg
n. (context US English) A container for beer holding 7.75 US gallons, equal to half the size of a standard beer keg.
Usage examples of "pony keg".
When he saw me, he began hoisting a pony keg out of the cold well I'd had installed with the proceeds of the Starke case.
Puddle swung a pony keg onto the bar, grabbed the biggest mug he had, drew me one.
I had to leap right over the image of the wake itself-french fries and a pony keg.
A paddle-tipped tentacle as big around as a pony keg curled out of the water and wrapped itself around the net-tender.