We're going to Florida for a winter vacation soon. I'll be taking a fixed 18.5 on a compact APS-C camera. Its FF equivalent is 28mm.
For APS-C Canon: EFS 15-85 for "full frame" EF 24-105 Not perfect, but just "very, very" handy. so famous it has a cup made in its image
Feel the need to revise my answer. If I was allowed only one lens, I most likely would stop photographing altogether or focus on avian and airshow photography: that'll be the 200-500 on a D500. But what really is the point of being allowed only one lens? Especially if the OP doesn't seem to be able adhere to that self-imposed limit himslef, so why should anyone else? How about asking a painter to be limited to one brush, or a sculptor to one particular tool only.
OP <br> Is the idea to travel as light as possible? <br> Because that is a completely different discussion, as the choice of camera itself comes into play.