Theme: How's the Grub, Bub? - The theme seems right up front but the unifier reveals an extra tidbit.
20A. On-the-go morning snack : BREAKFAST BAR
37A. Cash for a sandwich : LUNCH MONEY
43A. Waiter's handout : DINNER MENU
57A. Familiarly, nutritious trio found twice in this puzzle : THREE SQUARES
Argyle here. I never completely read the the unifier and so I was surprised to find circles in three corners of the puzzle. Some of you may not have gotten these circles. In the NE, SE, and SW corners, the word MEAL forms a little square. See here.
There are at least two different theories on where we got the phrase, a square meal. One is that it comes from the wooden board that served as a plate.
The other comes from the idea that a square meal was an honest, fair meal. Square is used in the sense of getting a square deal. Three hots and a cot!
Across:
1. Onetime VHS rival : BETA. Both are gone now.
5. Like honed knives : SHARP
10. Relaxed : CALM
14. The Earth turns on it : AXIS
15. Swiss calculus pioneer : EULER. Leonhard Euler, 1707 – 1783, was a pioneering Swiss mathematician and physicist.
16. Hebrides hillside : BRAE. The Hebrides is the archipelago off the west coast of Scotland. Map.
17. Rules, in brief : REGS. Regulations.
18. Grassy Southwestern tract : LLANO
19. "Mike and Mike in the Morning" radio station : ESPN. Check your local listings.
23. Flight that may be round : TRIP
24. Craft stabilizer : KEEL
25. "¡No __!": Mexican's "Enough!" : MAS. A phrase made famous in the Roberto Duran vs. Sugar Ray Leonard fight.
28. Story spanning decades : SAGA
31. St. Teresa's home : ÁVILA. Ávila is the capital of the province of the same name in the center of Spain.
33. Matador's cloak : CAPA
40. Tenth of a sawbuck : ONE CLAM
42. Tailgaters' beverage carriers : COOLERS
45. Dorothy's dog : TOTO
46. Run the show : EMCEE. Used as a verb.
47. Vidal's Breckinridge : MYRA. Myra Breckinridge is a 1968 satirical novel by Gore Vidal written in the form of a diary. It was made into a movie in 1970.
49. Actress Sandra : DEE
50. Moan and groan : CARP
53. Browning work : POEM
61. Dubai big shot : EMIR
64. Medium's card : TAROT
65. Part of a float : SODA
66. Take it easy : LAZE
67. Bacteria in rare meat : E. COLI
68. Footnote word : IDEM. "the same". Ibid.(short for ibidem), means the same place.
69. Biblical heirs, with "the" : MEEK
70. Barber's chair attachment : STROP. The leather strap used to sharpen a straight edge razor.
71. Corporate __ : SEAL
Down:
1. Farm fence feature : BARB
2. Put into action, as effort : EXERT
3. LSU mascot : TIGER
4. Very, musically : ASSAI
5. __-centered: egotistical : SELF
6. Luau entertainment : HULA
7. Sarah Palin, notably : ALASKAN
8. Yvonne's income : RENTE. French.
9. Legislative investigation : PROBE
10. "Good buddy" : CBer
11. Horace's "__ Poetica" : ARS. Also known as "The Art of Poetry".
12. Comfy spot for some cats : LAP
13. Guys : MEN
21. GI mess crews : KPs. Kitchen Police; fits with today's theme.
22. Memorable Texas landmark : ALAMO
25. "Giant" actor Sal : MINEO
26. Ready for whatever : ALERT
27. Final authority : SAY-SO
29. Old apple spray : ALAR
30. Frances __: Judy Garland's birth name : GUMM
32. Battery unit : VOLT
33. Encrypted : CODED
34. Japanese cartoon style : ANIME
35. Pound divisions : PENCE. Since decimalisation in 1971, the British pound has been divided into 100 pence.
36. Adolescent woe : ACNE
38. Manhattan campus, for short : CCNY. City College of New York.
39. Rush __ : HOUR
41. Bloodsucker : LEECH
44. Invisible-clothes wearer in an Andersen tale : EMPEROR
48. "The Simpsons" storekeeper : APU
51. José's humanities : ARTES
52. Show one's feelings, say : REACT
54. Kalahari refuge : OASIS. Southern Africa.
55. Wear away : ERODE
56. Jason jilted her : MEDEA. The cad!
57. Taxing trip : TREK
58. Go it alone : SOLO
59. You may stick it in your ear : Q-TIP
60. Dan'l's cousin? : SAM'L. And they ride on a cam'l.
61. Street shader : ELM
62. Ginnie __ : MAE
63. Special ending? : IZE. Specialize.