Theme: We'll Get Along Swimmingly or This Puzzle Is All Wet. You can choose.
It will make more sense if we start with the unifier.
1. Natural sand bank: BERM. A flat strip of land, raised bank, or terrace bordering a river or canal. I guess it could be sand.
5. Historic times: AGES. As, free, the jazz AGE.
9. Standing at attention, say: ERECT. Upright, as a good soldier should be.
14. Diva's solo: ARIA. From operas and oratorios. If Game of Thrones were an opera there could be an Arya ARIA.
15. Meter starter: DECI-. Meaning one tenth of.
16. Cookie maker's tool: MIXER. To blend all the ingredients
20. "Jeopardy!" contestant: ASKER. That's the way this show works. Answers must be in the form of a question.
21. Cub slugger: SOSA. Samuel Peralta Sosa [b 1968] is a Dominican American former professional baseball right fielder. He played in Major League Baseball for 19 seasons, primarily with the Chicago Cubs. After playing for the Texas Rangers and Chicago White Sox, Sosa joined the Cubs in 1992 and became regarded as one of the game's best hitters. [Wikipedia]
22. Paradise: EDEN. The perfect place, if you can keep it.
23. Anasazi home setting: MESA. A table land in the American South-west. The Ancestral Puebloans, also known as the Anasazi, were an ancient Native American culture that spanned the present-day Four Corners region of the United States, comprising southeastern Utah, northeastern Arizona, northwestern New Mexico, and southwestern Colorado. [Wikipedia]
25. "__ the season ... ": TIS. To be jolly, so cheer up, dammit!
27. Crowd no., often: ESTimation.
33. It's its own square: ONE. Also the loneliest number.
34. Nice water?: EAU. French. Do you think it's nice?
35. Lanai greeting: ALOHA. Welcome to Hawaii
44. Enjoying a scone, maybe: AT TEA. We have tea at 4:00 every afternoon. Sadly, though, I have to watch my carbs.
45. Call to Jude?: HEY.
52. African snake: ASP. As Cleopatra well knew, as the story goes. But historians dispute the manner of her death
55. Major NJ airport: EWR. Newark - Liberty International Airport.
56. Prepare to mail: SEAL. As an envelope.
57. Small deer: ROES. These are small deer native to Europe, reddish and grey-brown, and well-adapted to cold environments.
59. NYC's __ River: EAST. A salt water tidal estuary in New York City. The waterway, which is actually not a river despite its name, connects Upper New York Bay on its south end to Long Island Sound on its north end. Who knew?
61. Salamanca snacks: TAPAS. Salamanca, in northwestern Spain, is the capital of Salamanca province, part of the Castile and León region. Appetizers or snacks in Spanish cuisine.
68. Frisky swimmer: OTTER. Some aquatic creatures are fish. others are otters. Either way, they're all wet.
69. "The Clan of the Cave Bear" protagonist: AYLA. The Clan of the Cave Bear is a 1980 novel and epic work of prehistoric fiction by Jean M. Auel about prehistoric times. It is the first book in the Earth's Children book series, which speculates on the possibilities of interactions between Neanderthal and modern Cro-Magnon humans.
70. Fencing tool: EPEE. A sharp-pointed dueling sword, designed for thrusting and used, with the end blunted, in fencing.
71. Feature of Mike and Ike candy?: RHYME. Oblong, chewy, colorful candies coming in many flavors. The only rhyming aspect I can figure out is in the name.
72. Pour: TEEM. TEEM means to be full of or swarming with. I can't relate it to pour.
73. Look after: TEND. As sheep or children.
Down:
1. Quick Draw's sidekick __ Looey: BABA.
3. "Casablanca" hero: RICK. Also classic.
5. Turmoil: ADO. A state of agitation or fuss, especially about something unimportant.
6. Enjoys the beach, say: GETS A TAN. Don't forget your sunblock. You want a TAN, not a burn.
7. Canyon comeback: ECHO.
8. Afternoon break: SIESTA. Nap in Spanish
9. Long-legged runner: EMU. Big bird.
10. Serious ceremony: RITE. By definition
11. Radiate: EXUDE.
12. Roman goddess of agriculture: CERES. In ancient Roman religion, Ceres was a goddess of agriculture, grain crops, fertility and motherly relationships. [Wikipedia]
18. Plant with a trunk: TREE.
19. Gladly, to Shakespeare: FAIN. Archaic word meaning done with pleasure.
24. Old-time knife: SNEE. A large knife. The word has cognates in other Germanic languages.
26. Sign of surgery: SCAR.
28. Pop at a counter: SODA. Pop in some regions, soda in others. or even soda pop. What do you say?
29. Down but not out: IN IT. As, for example, the Chiefs with 14 seconds left.
30. Slick: DEFT. Said of something done in a neatly skillful and quick manner, as for example Matthew Stafford to Cooper Kupp, as can be seen here.
31. Babe and a doctor: RUTHS. Baseball star George Herman Ruth, Jr. [1895 - 1948] and Dr. Karola Ruth Westheimer. [b. 1928]
32. "Do Ya" rock gp.: ELO. Electric Light Orchestra.
37. "You are __": mall map info: HERE.
38. Exec.'s helper: ASST. Assistant.
40. Big mo. for chocolate purchases: FEB. Thank you, St. Valentine.
41. Steakhouse order: RARE. Style of cooking.
42. Established method: SET STYLE. I'd call a standard operating procedure, but OK.
43. Work at a keyboard: TYPE. As I am doing right now.
48. Pretty pitcher: EWER. A large jug with a wide mouth. Might or might not be pretty as a picture.
49. 1994 Peace co-Nobelist with Rabin and Peres: ARAFAT. Mohammed Abdel Rahman Abdel Raouf al-Qudwa al-Husseini [1929 - 2004] popularly known as Yasser Arafat or by his kunya Abu Ammar, was a Palestinian political leader.
50. Solemn vow: OATH.
51. Brit's Bordeaux: CLARET. Unofficial reference to red Bordeaux wines.
52. Garden recess: ARBOR. A shady garden alcove with sides and a roof formed by trees or climbing plants trained over a wooden framework.
53. TV's "__ Park": SOUTH.
60. Roy Rogers' birth name: SLYE. Leonard Franklin Slye [1911- 1998] aka Roy Rogers was an American singer, actor, and television host. Following early work under his given name, first as co-founder of the Sons of the Pioneers and then acting, the rebranded Rogers then became one of the most popular Western stars of his era.
63. "Right you are!": AMEN.
64. Went too fast: SPED.
66. Before, to a poet: ERE.
67. Yosemite __: SAM.