Consistent with Mari-Lou A's excellent answer, Google Books and Elephind newspaper database searches yield no earlier matches for the expression attributed to Don Meredith in 1970:
If "ifs" and "buts" were candy and nuts, we'd all have a merry Christmas.
However, Elephind does find a somewhat similar (and significantly earlier) sing-song rhyme about "ifs and buts" from Australia. From "They Spoil Everything," in the Perth [Western Australia] Sunday Times (March 14, 1937):
Were "Ifs" and "Buts"/ Just tents and huts,/ How gaily could we hide!/ If "Buts" and "Ifs"/ Were yachts and skiffs/ How merrily we would ride!/ But "Ifs" and "Buts"/ They Interfere/ And spoil the whole affair./ If it were not/ For "Ifs" and "Buts"/ I'd be a millionaire!
It seems unlikely that Meredith (who grew up in a small town east of Dallas, Texas; went to college at Southern Methodist University in Dallas; and spent his entire NFL playing career with the Dallas Cowboys) had ever heard the "tents and huts" rhyme before sharing his "candy and nuts" rhyme on TV, but I suspect that he didn't invent his version either. It's the sort of deflating thing that parents and schoolteachers tell children to bring them back down to earth.
'Ifs and buts' before 'candy and nuts' or 'tents and huts'
The phrase "ifs and buts" appears in Google Books search results going back to Luther Martin, Modern Gratitude, in Five Numbers: Addressed to Richard Raynal Keyne, Esq. Concerning a Family Marriage, which includes this outraged footnote:
- Precious Hypocrite! "Who with Ifs and Buts would damn fair fame."
I haven't been able to find a source for the sentence that Martin puts in quotation marks.
An Elephind search discovers another seemingly aphoristic expression involving "ifs and buts." From an advertisement headed "Ifs and Buts" in the New-York Daily Tribune (June 20, 1910):
The ifs and buts of life are thicker than confetti at a fair.
Far more common (especially in content from Australian sources) are doggerel/jingle rhyming of "ifs and buts" with "nuts" (or "ruts" or "guts"). From "Old Fashioned Eats," in the [Valley City, North Dakota] Weekly Times Record (August 16, 1917):
No arguments/ With ifs and buts,/ Will e'er excuse/ Such meatless nuts.
From "Gay Adventures," in the Maitland [New South Wales] Daily Mercury (April 11, 1935):
Are you afraid to adventure? Haunted by "ifs" and "buts"? Then how can you hope for the sort of success that's not to be found in ruts? If never a risk you're taking—if you gaze at fortune's tide, and ponder too long your chances—in safety-rut you'll bide!
From "Obvious," in the [Perth, West Australia] Sunday Times (October 1, 1939):
A London society paper states that as a result of the war the usual "nuts" are entirely absent from the swagger cafes in Piccadilly.
Though by ifs and buts/ We're oft repelled,/ May we say that the nuts/ Are away being shelled!
And from "We Australians," in the [Charters Towers, Queensland] Northern Miner (January 29, 1940):
We're a nation young, a nation small,/ Maybe perhaps you're right/ That distance makes our help a pall/ In England's present plight./ We're a nation gay of "ifs and buts"/ "That fool around in mobs,"/ We're a nation, too, that has the guts,/ Minus in titled snobs.