In Avengers: Infinity War, when Spider-Man is clinging to the outside of The Maw's ship as it's leaving Earth, Iron Man provides Spider-Man with a new suit.
Just as Spider-Man exclaims how cool the new suit is, Tony has F.R.I.D.A.Y. deploy a parachute that's a part of Spider-Man's suit, to get Peter back to Earth. Well, right after Tony commands F.R.I.D.A.Y. to deploy the chute, and Peter gets sucked away, Tony yells to Peter:
"Happy trails, kid!"
To me, this seems like it might be a reference to something, and I'm thinking a movie, since one of the recurring elements between Peter and Tony in this film is making movie references. But, I've tried searching for the reference and have been unsuccessful so far.