1. Stuff of little substance → FLUFF
2. What matching ends of magnets do → REPEL
3. Like 20 Questions questions → YESNO
4. Person who might have the other half of a heart necklace, in brief → BFF
5. In the manner of → ALA
6. Nabisco wafer brand → NILLA
7. Longtime Supreme Court justice Frankfurter → FELIX
8. On the house → FREE
9. Baseball's Gehrig → LOU
10. Words set in stone? → EPITAPH
11. Establishment with red, white and rosé options → WINESTORE
12. Knowing, as a secret → INON
13. "___ sells" (advertising catchphrase) → SEX
19. Campus courtyard → QUAD
21. Arrange from newest to oldest, say → SORT
25. Santa's landing spot → ROOFTOP
26. Service symbolized by a dot and three curved lines → WIFI
28. Believer in communism achieved through class struggle → MARXIST
30. ___ Romeo (sports car) → ALFA
31. Poet ___ St. Vincent Millay → EDNA
32. Breather → REST
33. Computer-controlled players, in gaming lingo → BOTS
34. Continental cash → EURO
35. Headed the cast of → STARREDIN
36. Weapons → ARMS
37. Luau garland → LEI
41. Ilhan of Congress → OMAR
44. "This cannot be stressed enough ..." → IREPEAT
46. Maori dance with rhythmic chanting → HAKA
48. "The Three Little Pigs" antagonist → WOLF
51. Full of passion → FIERY
52. One of seven won by "Oppenheimer" → OSCAR
53. Famous → NOTED
54. In the cooler → ONICE
55. Chemical element whose name starts with an 8-point Scrabble letter → XENON
56. What yeast makes dough do → RISE
58. Send-___ (farewells) → OFFS
60. Seasoning for una margarita → SAL
61. Ambient music composer Brian → ENO
62. "I wish I could unhear everything you just said!" → TMI
63. Mermaid's milieu → SEA