Some clues yield an extra letter (not to be entered in the grid) in their wordplay
1a Pull sled, ultimately one's own (3) looks like TOW but why?
11a Spending shilling, maybe lunch on 25th's steep for ancient Shetlander (4) ??UP "U" is dubious?!
..........25th could possibly be Y?
35a Worst cracker-joke essentially providing prospect of continuing enjoyment (5) ???SE