Attain dual citizenship. If one of your parents were born in a foreign country, you may have the right to become a citizen there…
It costs $49 but it pays for itself as you get your mile match with other airlines and many of Frontier flights are only 10-20K for a domestic flight.
Don’t rule out “positioning flights” when flying. But be sure to space the two separate flights with enough time to leave for any hiccups.
When cruising, I always bring my luggage to my cabin and do not check it. Sure, you must bring it onto the boat yourself, so it is 10 minutes of inconvenience for possibly hours saved later.