“Take all you want, but eat all you take” (sometime given as “Eat all you want, but eat all you take” or “Eat/Take all you can, but eat all you take”) was a food conservation slogan used in the United States armed forces in 1943, during World War II. The slogan was printed on mess hall posters. After the war, the slogan appeared on posters and on menus at cafeterias and other restaurants.
 
The slogan pre-dates the 1943 World War II mess hall posters. In a 1939 column, Walter Winchell wrote that there was a rule at the Alcatraz prison (San Francisco, CA) cafeteria: “Take all you want—BUT eat all you take!” Google Books (which often has incorrect dates) appears to show 1941 and 1942 citations of the phrase; the 1941 usage is from a college campus.
 
   
Yahoo! Answers
Is it okay to take food home from all you can eat buffets?
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Generally buffet style restaurants don’t allow people to take food home. A regular restaurant gives out predetermined portions to people who paid for them. If you want more you have to reorder and pay for it. Whether this food is consumed on the premises or taken home is up the paying customer.
 
At all you can you can eat buffets generally the rule is “take all you want but eat all you take”. Otherwise they’d go out of business.
     
22 November 1939, Wisconsin State Journal (Madison, WI), “On Broadway With Walter Winchell,” pg. 4, col. 5:
One of the strictest rules at Alcatraz is the rule about food. The food is served cafeteria style, and there’s plenty of it. The rule, however, is, “Take all you want—BUT eat all you take!”
       
Google Books
University Administration Quarterly: For College and University Officials
Published 1941
Item notes: nos. 1-2
Pg. 366:
On another campus, the emphasis was on food, but this time on its conservation. “Take all you want, but eat all you take” was the slogan at all campus eating places.
   
Google Books
Jahco News
By Jack and Heintz, Inc
Published by Jack & Heintz, 1942
Item notes: v. 3, nos. 5-11
With the food shortage as it is today, a good slogan would be “Take All You Want to Eat, but Eat All You Take.”
   
7 February 1943, Abilene (TX) Reporter-News, “Rationing of Food Practiced for Men in U.S. Armed Forces” from Office of Price Administrator, pg. 8, cols. 5-6:
In the Navy food conservation takes a similar turn. Afloat the authorities emphasize the theme of “take all you want, but eat all you take.” The Navy uses a series of eight posters to illustrate this message. One shows an overloaded garbage can wearing Hitler’s face. It says—“The food we eat helps us win—the food we waste makes Hitler grin!”
 
14 March 1943, Lubbock (TX) Avalanche-Journal, “Field Rations Give Men At LAFS Taste Of Food Rationing,” pg. 12, col. 4:
“Eat All You Take”
“Eat all you want, but eat all you take” has long been more than a slogan at LAFS (Lubbock Army Flying School—ed.), and the man who lets his eyes prove “bigger than his stomach” has always been in danger of drawing an assignment to KP as punishment.
 
7 April 1943, Christian Science Monitor, second section, pg. 13:
Navy Orders: Feed Your Stomach, Not Your Eyes
Take all you want, eat all you take, men are told in move to prevent any wastage of food.
Officers Are Cautioned Food Where Needed
By a Staff Correspondent of The Christian Science Monitor
WASHINGTON—“Take all you want but eat all you take,” is the Navy’s new slogan against food waste at shore stations in the United States.
       
10 December 1943, Yank, The Army Weekly, pg. 10, col. 1:
About the buffet in the dining room was the bold-faced reminder on food conservation: TAKE ALL YOU WANT, BUT EAT ALL YOU TAKE.
 
Google Books
Food engineering
Published by Chilton Co., 1943
Item notes: v. 15
Pg. 48:
As a move to avoid waste of food, the Navy is telling sailors to “take all you want to eat, but eat all you take.”
       
Time magaine
Ike’s Appetite
Monday, May. 29, 1944
One noontime last week General Eisenhower inspected huge, noisy “Willow Run.” the mass-production officers’ mess in London’s swank Grosvenor House. Refusing a table in the alcove reserved for rank, General “Ike” joined a line of junior officers at the cafeteria. In due course he collected pork, potatoes, spinach and salad.
 
Presently the Supreme Commander, full and beaming, swigged the last drop of coffee and pushed back his half-eaten meal. He had broken his own rule. A tactful escort murmured about the mess regulation on food economy, which is enforced by slips inscribed: “Eat all you take on your plate or explain by endorsement here-on.”
   
Google Books
Convention proceedings
By United Electrical, Radio and Machine Workers of America, United Electrical and Radio Workers of America
Published by United Electrical, Radio and Machine Workers of America., 1944
Pg. 246:
In the mess hall where we go into eat they say to us, the Army wants you to eat all you want, eat all you can, but eat all you take.
     
Google Books
Good food and nutrition for young people and their families
By Edna Phyllis Amidon, Dorothy Edith Bradbury and Vivian V. Drenckhahn
Published by J. Wiley & Sons, Inc.
1946
Pg. 212:
The slogan, “Take all you want but eat all you take,” ...
 
Google Books
May 1949, Baseball Digest, pg. 61:
At seven A. M. police whistles aroused them in the barracks where they slept and they breakfasted in a cafeteria where a sign warned, “Take all you want, but eat all you take.”
       
Google Books
Let’s Get Our Money’s Worth:
Army Troop Information Discussion Topics
Dep. of the Army Pamphlet No. 20-133.
Published by s.n., 1951  
Pg. 6:
The World War II motto, “Take all you want, but eat all you take,” is a good one to follow.
 
Harvard Crimson
All You Can Eat
The Foodgoer
Published On Thursday, March 24, 1955 12:00 AM
By THE WALSUS
With tenderloin whale steak in season, all true smorgasborders should visit Ola’s Norweigian restaurant at 16 Carver Street. Those who don’t like whale meat, or can’t remember how they roasted reindeer or potted ptarmigan in the old country might still enjoy some varied tastes. Just pass through the wrought-iron gates into the restaurant.
 
Inside, a portrait of the blond, blue-eyed proprietress smiles down from above the hearth at the waiters rushing between nine tables and an array of smorgasbord in the middle of the room. When the aroma and the candlelight have created the proper mood, grab a plate and sample the display of food. “Take all you can eat, but eat all you take,” is the menu’s advice. Ignore it.
   
Google Books
No Bugles, No Drums
By Charles Durden
New York, NY: Viking Press
1976
Pg. 6:
A big sign hung over the steam tables: TAKE ALL YOU WANT — BUT EAT ALL YOU TAKE.
     
NYTimes.com: Freakonomics Blog
May 9, 2007, 10:14 am
A Gluttony Tax
By Stephen J. Dubner
We’ve blogged before about a pay-what-you-wish coffee shop and pay-what-you-wish downloadable music. Now Luciana Silvestri, a reader from Argentina, writes with news of something different: An all-you-can-eat restaurant with a prix fixe twist. As she explains:
 
A friend has just returned to Argentina from a six-month internship in Chicago and told me about a Japanese restaurant with quite an original pricing system. The restaurant is called Sushi Para II. The address is 2256 N. Clark, Chicago. Apparently, you can consume all the sushi you want for something like $17, but if you leave anything on your plate, you must also pay for leftovers. This creates an incentive to eat a lot but to order in the right measure. I wonder how many people actually accomplish to leave the place with no surcharge AND no tummy ache.
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COMMENTS
6. May 9, 2007
10:46 am
There is a buffet here in MN with a sign that says “Take All You Want, Eat All You Take, Extra Charge for Wasting.”
 
I asked about it once and the manager said its for kids who’s eyes are bigger than their stomachs. They don’t really charge, but they “warn” the kids about next time.
 
I wonder how often (if at all) its enforced there?
— 711buddha
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19. May 9, 2007
4:48 pm
@6 -
That was exactly the rule posted in the enlisted mess when I was an army draftee: Take all you want, but eat all you take. No extra charge, but they had other ways of making you pay. 😉
— Mack
 
Laura On Life
Golden Eating Rule
Friday, 09 January 2009 12:37
I used to think there was only one way to eat.  When I was growing up, there were lots of rules where eating was concerned and those rules, I thought, narrowed down the choices as to the things you could do while eating.  We employ many of the same rules, but only one Golden Eating Rule:  Take all you want, but eat all you take.