Soaring Insignia

Infinite flight, but only if you already own something that flies. This is not a pair of wings. Bolt it onto wings or Rocket Boots and the fuel gauge stops existing. Wear it alone and you get sharper acceleration and a higher jump, which is pleasant and not what you came for.

Wings that were unusable because they ran dry in a second or two become viable again, and the Jetpack is the clearest case, since low fuel was its only real flaw. Hover wings pair well for the same reason: you no longer need an infinite flight mount just to hold position above a boss. The acceleration and jump bonuses are large enough that the cheap pre-Hardmode jump accessories still contribute alongside it, which almost nothing else this late in the game can say.

Mounts ignore it almost completely, so swapping to one throws the benefit away. Rocket Boots flying forever does not mean you stop taking fall damage, and that catches people the first time they run out of altitude. The Flying Carpet gets the handling improvements without the endless flight. Equipping it midair after burning your flight refills Rocket Boots but not wings, unless you happen to be wearing all of it at once.