it means basically 'cash and carry'... you pay someone cash on the spot (placing the cash atop a barrel that's for sale) and they in turn release the goods to you right then and there - and you carry it (the barrel) away!
I see that you're selling your car on line. Can I give you cash on the barrel head and I drive away with the title?
also "cash on the barrelhead". Means that you give me cash, and I'll give you the product at that time. No credit no delivery.
Buddy: You ever think about selling that old juicer?
Barbara: I'll give it to you for $20 - cash on the barrel.
Buddy: OK, here is the money.
Barbara: Thank you, here is the juicer.
Buddy: It has been a pleasure doing business with you.
Barbara: The feeling is mutual.
A Shackteau is a humble, weather-beaten, structurally questionable shelter located in a spectacular or highly coveted place—Wales, Jackson Hole, Sun Valley, Crested Butte, coastal Maine, the Alps—where the building itself may be worth almost nothing, but the dirt, view, access, and mythology make it absurdly valuable.
In use:
Shackteâu - We thought it was an abandoned shed until the realtor called it a rare alpine Shackteâu with unobstructed views and listed it for $2million.