+1 for the
Cussler books. His slightly older books are better than the new ones he puts his name on with another author imho. There are quite a few Dirk Pitt novels out there, so they are good as most airports have another one if you finish the one you have. I didn't like the very early Dirk Pitt's nearly as much as a few books into the series. These do make great plane and vacation reading.
Dean Koontz does several great series...the newer Odd Thomas books are great. Some of his earlier books delve into the "unknown" in a different way and I think they are also excellent reads. My hubby doesn't like these as much as I do...too much esoteric stuff, I think.
If he hasn't read them or hasn't read them in a while,
Tolkein's (Lord of the Rings, the Hobbit) are nice coz you can get totally immersed in them and time flies...and LOR series is LONG
Crime fiction is always good holiday fodder: check out
James Patterson,
Kathy Reichs, the
Kellermans (Jonathan and his wife, whose name I forget, write separately so lots of books to choose from)
Dark humour also makes my list of reads for holiday travel - no one does it better than
Carl Hiassen.