“Take half as many clothes and twice as much money as you think you’ll need for any vacation” is an established travel axiom. The saying probably originated in Reader’s Digest for June 1949:
 
“MY AUNT’S sage advice for vacationers: ‘Decide on all the clothes and all the money you will need; then take half the clothes and twice as much money, and you will have a wonderful holiday.’ — Contributed by Mrs. F. C. Bingham”
 
A similar saying is “Backpacking:  An extended form of hiking in which people carry double the amount of gear they need for half the distance they planned to go in twice the time it should take.”
 
 
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The Reader’s Digest
Volume 54
1949
Pg. 49:
MY AUNT’S sage advice for vacationers: “Decide on all the clothes and all the money you will need; then take half the clothes and twice as much money, and you will have a wonderful holiday.” — Contributed by Mrs. F. C. Bingham
 
24 June 1949, Mason City (IA) Globe Gazette, pg. 30, col. 2:
A current magazine offers this counsel to vacationers: Decide on all the clothes and all the money you will need; then take half the clothes and twice as much money—and you’ll have a wonderful time.
 
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20,000 Leagues Behind the 8 Ball
By David Dodge
New York, NY: Random House
1951
Pg. 7:
Whoever the genius was who recommended that the traveler take half as much baggage and twice as much money as he thinks absolutely essential, he spoke pearls of pure wisdom.
 
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You Can Profit from Stress
By Gary R. Collins
Santa Ana, CA: Vision House Publishers
1977
Pg. 206:
There are two other rules for vacations: first, don’t take any work along, and second, take half the clothes and twice as much money as you think you will need!
 
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The New Zealand Way
By V. F. Wilkinson
Christchurch, N.Z. : V.W. Pub.
1981
Pg. 202:
My first bit of advice to would-be travellers is an old one, “Take half as many clothes and twice as much money as you think you will need.”
 
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The Complete Murphy’s Law:
A Definitive Collection
By Arthur Bloch
Los Angeles, CA: Price Stern Sloan
1990
Pg. 220:
STITZER’S VACATION PRINCIPLE:
When packing for a vacation, take half as much clothing and twice as much money.
     
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April 1990, American Motorist, pg. 50, col. 2:
Finances:
How much should you bring along?
Traditional wisdom says you should always take half as many clothes and twice as much money as you think you’ll need on any trip.
 
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On Your Own in El Salvador
By Jeff Brauer, Julian Smith and Veronica Wiles
Charlottesville, VA: On Your Own Publications
1995
Pg. 49:
Packing
Two words: pack light. Heed the old correspondent’s axiom: “Lay out everything you think you will need on the bed, then take half of that and twice as much money.”
 
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Home Sweeter Home:
Creating A Haven Of Simplicity And Spirit
By Jann Mitchell
Hillsboro, OR: Beyond Words Publishing, Inc.
1996
Pg. ?:
Remember the traveler’s axiom: Take half the clothes you think you’ll need—and twice as much money!
 
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The Complete Live and Learn and Pass It On:
People Ages 5 to 95 Share What They’Ve Discovered About Life, Love, and Other Good Stuff
By Jackson Brown
Nashville, TN: THomas Nelson,. Inc.
2007
Pg. 174:
I’ve learned that when packing for a vacation, you should take half as many clothes as you think you will need and twice as much money. Your clothes and money should run out at about the same time! —AGE 55