Theme: This One is for Beetle Bailey - Key letters from the reveal begin the theme entry words.
53A. Military mess assignment, and this puzzle's title : KP DUTY
6D. Tot's wading spot : KIDDIE POOL
10D. Deli sandwich freebies : KOSHER PICKLES
18D. Decisive end to a boxing match : KNOCKOUT PUNCH
30D. Rustic paneling wood : KNOTTY PINE
Argyle here. Rabbit, rabbit. Bit confusing for a Monday. Four columns for the main entries and an across for the reveal. Until I replaced TATER with TUBER, my SE corner would not fill. A challenging Monday.
Across:
1. Toast go-with : JAM
4. Its pH is more than 7 : ALKALI. Less than 7 is acidic.
10. Queen's spouse : KING. Too easy, didn't trust it.
14. "__ live and breathe!" : AS I
15. Spoil, as a barbecue : RAIN ON. Let's hope it won't rain on your parade Thursday.
16. Most eligible to be drafted : ONE A
17. Conceded the point : BACKED DOWN
19. Sean Connery, by birth : SCOT
20. Connected the opposite shores of, as a river : SPANNED
21. Flammable gas : ETHANE
23. Caravan's watering hole : OASIS
25. Feel remorse over : RUE
26. Like-minded groups : BLOCS
29. Yosemite grazer : ELK. I'm not sure of the location but it's pretty.
Update: Yosemite no longer has grazing elk. This elk is in Great Sand Dunes National Park and Preserve, CO.
31. Cattle marking : BRAND
35. Geologist's collectible : ROCK
36. Backbone : SPINE
38. Fishing spot : PIER
39. Turnpike traveler : AUTO
40. With 69-Across, Dr. Seuss classic : HOP ON. 69A. See 40-Across : POP
41. State where Interstates 35 and 80 cross : IOWA
42. Prie-__: kneeler : DIEU. Has this become a Monday word?
43. Receives guests : HOSTS
44. Symbol before the sharps and flats : CLEF
45. Dust-up : SET TO
47. Way past tipsy : LIT
48. Dress bottom : SKIRT
49. Influential D.C. group : PAC
51. Medication for insomniacs : NYTOL. Brand name.
56. Developmental stage : PUBERTY
60. Sentence subject, as a rule : NOUN
61. "Is that a guarantee?" : "CAN I BE SURE?". Hah!
64. Oil cartel acronym : OPEC
65. Repair shop courtesy : LOANER
66. Wire thickness unit : MIL
67. Second-youngest March sister, in literature : BETH. "Little Women"
68. __ Glue-All : ELMER'S. Another brand name.
Down:
1. They set up the 18-Down : JABS 18D. Decisive end to a boxing match : KNOCKOUT PUNCH. (in case you forgot)
2. Quickly, in memos : ASAP
3. Flaky mineral : MICA
4. Sports venues : ARENAs
5. Puts on cargo : LADES
7. 12 months in Madrid : AÑO. Update: Tilde added thanks to PaulG's comment. Perhaps I've learned my lesson.
8. Close to the ground : LOW
9. Word before circle or peace : INNER
11. Ancient Peruvian : INCA
12. Eye-catching sign : NEON
13. Airport boarding area : GATE
22. Bathroom fixture : TUB
24. Enters stealthily : SLIPS IN
26. Thin nails : BRADS
27. Huey and Dewey's brother : LOUIE. Donald's nephews.
28. Four pairs : OCTET
32. Garlicky sauce : AIOLI. Mayo with attitude.
33. More modern : NEWER
34. Preliminary version : DRAFT
36. Librarian's admonition : [SHH!]
37. Nav. officer : ENS.
46. Bit in a horse's mouth? : OAT. A bit is part of the bridle that goes in the horse's mouth.
48. Recovers from a bender, with "up" : SOBERS
50. Washer phase : CYCLE
52. Yam, for one : TUBER
53. Handle near a keyhole : KNOB
54. Francis or John Paul II, e.g. : POPE
55. Song for two : DUET. 58D. Song for three : TRIO
57. Beef cut : RUMP
59. Shrill cry : YELP. This got me; I had YELL.
62. Internet giant that owns MapQuest : AOL
63. '60s combat venue, briefly : NAM
Argyle
