I used to optimistically pack workout clothes with me whenever I went on a trip (business or pleasure), and over time I’ve learned that I never ever use them, so now I leave them at home and I rely on the strength of my home workout routine to tide me over while I’m away.
I also think that the stress (often the exciting good stress) of travel can use up some calories anyway. The one thing I bring no matter what is a swimsuit, because to me swimming isn’t a boring workout chore; it’s a fun thing to do. I also try to bring a robe with me because many of the hotels I stay at don’t have them, and especially when I’m traveling with work colleagues, I think they appreciate it when I don’t answer the door naked. This allows me to work from bed on the road if the situation allows, while still being able to throw on something semi-appropriate when room service comes.