“One for the road” usually means that a person wants a drink at the bar before commencing on a long journey (such as on a train or an airplane, or a car that he or she is not driving). A classic bar joke has a man walking into a bar with a slab of asphalt under his arm. “A beer for me, and one for the road,” he tells the bartender.
 
“A man walks into a bar with a slab of tarmac under his arm…” was cited in print in 2001.
 
   
BBC News
Monday, 10 September, 2001, 09:03 GMT 10:03 UK
What is the world’s funniest joke?
(...)
A man walks into a bar with a slab of tarmac under his arm. He chooses a table, carefully puts the tarmac on one of the chairs and walks up to the bar. “I’ll have a pint of lager”, he says to the barman before indicating to the tarmac “And one for the road”.
Tim, London
 
Google Groups: rec.humor
Hit The Road!
Zevra and his little green guy
12/12/01
Hit The Road! So, this guy walks into a bar right; which is pretty stupid come to think of it!
 
>Jude wrote:
>A guy walks into a bar with a hunk of pavement under his
>arm.
>
>The bartender looks at the pavement for a bit and then
>finally says, “What’ll ya have?”
>
>The guys says, “One for me and one for the road.”
>
OBBJ:
(Obligatory Bar Joke)
 
Google News Archive
21 December 2001, Gainesville (FL) Sun, “World’s funniest jokes revealed: An experiment named Laughlab took votes from 100,000 people” (AP), pg. 13A, col. 1:
Women preferred jokes involving word play such as: “A man walks into a bar with a piece of tarmac under his arm. He says to the bartender: ‘A pint for me, and one for the road.’”
 
Google Books
Arizona Liar’s Journal
By Jim Cook
Phoenix, AZ: Cowboy Miner Productions
2003
Pg. 147:
Chuck told about the groundhog who goes into a bar, carrying a little chip of asphalt between his teeth. He sets it on the bar and says, “Give me a drink, and one for the road.”
 
24 November 2003, Wisconsin State Journal (Madison, WI), pg. B1, col. 1:
A man walks into a bar with a slab of asphalt under his arm and says “A beer please, and one for the road.”
 
Google Books
The Biggest Joke Book Ever
By Jack Jacoby
Victoria, BC: Trafford
2008
Pg. 1007:
A man walks into a bar with a slab of asphalt under his arm and says, “A beer please and one for the road.”
 
Twitter
Col
‏@countcol
Old joke alert.
A man walks into a bar with a slab of asphalt under his arm.
“I’ll have a beer please.. And one for the road.”
2:21 PM - 4 Mar 2014