I've never seen a "beverage cooler" that can hold a half bbl. Most rental outfits may count on sixtels being used.
At events most craft brewers use 19 gallon "rope tubs" for their half bbls. Ice in the bottom, and a bag of ice on top. Placed in the shade if possible. Cover the whole rig with a blanket and/or some Reflectix if you want to keep it cooler and reduce ice use.
In lieu of rope tubs (Walmart?) you can probably use large totes instead.
As
@Closet Fermenter said, wrapping the keg with Reflectix definitely helps keeping it cold.
The bag of ice on top is important.
Some unsolicited tips:
- Count on being there early to set up and get things working to your liking.
- We spent about an hour Saturday setting up our club's 6-tap jockey box. There were 3 of us working on it, all very familiar with the ins and outs.
- Have enough CO2 on hand.
- Don't leave a spare gas tank in the car/truck! Heat blows...
- Bring your tools.
- Have signs for your booth, your beer, your brewery.
- Any swag on hand?