“How can you win a battle, if you don't arm yourself? Only a fool enters into a battle he cannot win.”

This is cited to Patton in Patton's Principles : A Handbook for Managers Who Mean It! (1982) by Porter B. Williamson as well as Leadership (1990) by William Safire and Leonard Safir, p. 47, but is also cited to Erwin Rommel‎ from his Infanterie Greift An [Infantry Attacks] (1937) in World War II : The Definitive Visual History (2009) by Richard Holmes, p. 128, and Timelines of History (2011) by DK Publishing, p. 392
Disputed

Free the Airwaves! (2002)
Context: The battle for the airwaves cannot be limited to only those who have the bank accounts to pay for the battle and win it. Democracy is in danger. Seats in Congress, seats in the state legislature, that big seat in the White House itself, can be purchased by those who have the greatest campaign resources, who have the largest bank accounts or own riches.
That, I submit to you, is no democracy. It is an oligarchy of the already powerful. It is no less than a conspiracy of the powerful to deny access to government to those who literally cannot afford to run for public office with any realistic hope of getting elected.

“No,” said the old man, deep under. “I don’t remember anyone winning anywhere any time. War’s never a winning thing, Charlie. You just lose all the time, and the one who loses last asks for terms. All I remember is a lot of losing and sadness and nothing good but the end of it. The end of it, Charles, that was a winning all to itself, having nothing to do with guns.
The Time Machine (1955)
R Is for Rocket (1962)

Variant translations
If you know others and know yourself, you will not be imperiled in a hundred battles; if you do not know others but know yourself, you win one and lose one; if you do not know others and do not know yourself, you will be imperiled in every single battle.
Know your enemy and know yourself, find naught in fear for 100 battles. Know yourself but not your enemy, find level of loss and victory. Know not thy enemy nor yourself, wallow in defeat every time.
Literal translation: Know [the] other, know [the] self, hundred battles without danger; not knowing [the] other but know [the] self, one win one loss; not knowing [the] other, not knowing [the] self, every battle must [be] lost.
Source: The Art of War, Chapter III · Strategic Attack

[David, Horowitz, http://archive.frontpagemag.com/readArticle.aspx?ARTID=17895, If You Would Rather Be Right Than President . . . Find Something Else To Do, FrontPageMagazine.com, June 3, 2003, 2016-02-12]
2003

This quote is widely attributed to Margaret Thatcher on various websites, and also appears in a number of books, including The Concise Columbia Dictionary of Quotations, Columbia University Press (1989), ed. Robert Andrews, p. 320 : ISBN 0231069901. 9780231069908 , but without any further source information such as date, location or any other context.
One valid Thatcher quote which may be the basis for the version above appears in the Second Carlton Lecture http://www.margaretthatcher.org/document/105799 (‘Why Democracy Will Last’), delivered at the Carlton Club, London (November 26, 1984) : Mr. Chairman, each generation has to stand up for democracy. It can’t take anything for granted and may have to fight fundamental battles anew. You know that marvellous quotation from Goethe : ‘That which thy fathers bequeathed thee / Earn it anew if thou would possess it.’
Thatcher also expressed this thought in a Speech to Atlantic Bridge (May 14, 2003) http://www.margaretthatcher.org/document/111266, delivered at the St. Regis Hotel, New York City : My friends, every generation has to fight anew the battle for liberty.
Disputed