First, I’m glad someone posted this. My pastor is not afraid to tell his congregation that we don’t take a vacation from Church in the summertime. Now, primarily, he is referring to those parishioners whose philosophy is, well, school is out, we are on vacation from Church, and he emphasizes that the Sunday obligation is an obligation every Sunday.
Second, Tarpeian Rock makes a good point. If one is on vacation in a city such as New York, Boston, Philadelphia, Minneapolis, or Washington, D.C., it’s pretty easy to find a Mass that will fulfill your Sunday obligation and fit into your schedule. (It might be a little harder in certain Southern cities, but I’m sure you can find a Mass).
Normally, I will make a Sunday Mass while traveling (unless I’m backpacking or out on a campsite an hour or more away from civilization), and I have sometimes flown home early enough (or my buddies and I make it home in time to clean up a little) to make a Sunday evening Mass. My city has one at 7:30 p.m., and quite a few others at 5:00 p.m., 5:30 p.m., and 6:00 p.m.)
About cruise ships…be a little careful. I’ve heard that some cruise lines are using priests from a “dissenting group” whose members were ordained years ago, but left the priesthood to marry. That said, you may not be getting a valid Mass, so you may want to do some research on the particular priest beforehand. I’m going on a cruise this summer with a group of friends and we will be in one port early Sunday morning, and plan to go to Mass in port.
Third, with summer starting, this is a good time to bring this up. I recall as a kid we would leave for Scout camp on Sunday morning, and most of the time my mom would take my brothers and I to the Saturday evening Mass, which fulfilled our Sunday obligation.