WOW That is a big question...
Minimally I have used a round Gott cooler, it holds a 3 or 5 gallon soda keg just fine. Surround the keg with ice and cover it with a damp towel. Use a hand pump to dispense the beer with a hand tap. drain the melted ice water as needed.
For more taps we bring a jockey box. Ours is a converted stainless Coleman cooler with dual taps and stainless coils inside. Hook the beer kegs up with a CO2 tank in line and fill the cooler with ice. Use a damp towel over the cooler and the kegs to keep everything cool. Be sure to turn off the CO2 tank when leaving, Many folks simply cannot resist an open tap.
Try this out at your next fest!
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