As for coming to Mass on vacation, if it’s on a Sunday or Holy Day of Obligation, this should not be a pleasant surprise, but rather something that is expected. You can’t take a vacation from God. Therefore, someone on vacation should be expected to wear the same thing they should wear at their home parish. It is not hard at all to pack a nice outfit, and many hotel room have irons and ironing boards to make your clothes look nice as well. I have been in this situation a few times in the past, so trust me that it can be accomplished without too much trouble.
If, however, they are going to a daliy Mass (i.e. not required), then that brings up the question of whether or not attire for Sunday Mass and daily Mass should be equivalent. I think I will start a new thread regarding that issue.
Finally, I agree with everyone who says that the way you prepare your clothes is important. I’m in Civil Air Patrol, and we wear what is basically the exact same uniform as the Air Force, aside from a few patches, badges, and insignia. The cadets who haved been promoted and reached high positions of authority do not have uniforms that look good because it is a requirement of their rank, but because the mindset of having a good appearance comes with the mindset of striving to take on leadership positions. Additionally, a good-looking uniform will draw respect from the fellow cadets, just as preparing your clothes for Mass will set a good example for fellow parishioners. Finally, when wearing the CAP uniform, we not only represent CAP but also the entire Air Force. If some random citizen sees a cadet wearing a uniform that is in bad condition, what impression will that make on them about the Air Force? Likewise, if someone sees you exiting Mass wearing sloppy clothing, what impression will that make upon them regarding the Catholic Church?
Well, I just thought I would add that in. Feel free to debate it. Take care and God bless.