Yeah... I have an omnibus edition of Wodehouse, but it seems a little cloying to read straight through. Best taken in small doses.
There is a big two-volume omnibus edition of Mark Twain that makes a good vacation haul-along.
If you haven't been through it yet, Neal Stephenson's Baroque Cycle (Quicksilver, The Confusion, The System of the World) is an amazing vacation-length read.
One of the best vacation reads that I ever had was a paperback edition of Isaac Asimov's non-fiction "Life and Energy." It's a very elegant 350 page undergraduate-level summary of the physical and chemical basis of "modern" biology. (As of 1962.) It's a bit dated now... I see the cover price of my copy is $1.25. Good grief, it was written before chemiosmotic theory! Anyway, I carried it along and read it during a hike on the Pacific Crest Trail when I was a teenager, and it just seemed very satisfying to stop on a mountaintop, or beside a stream and read a chapter. There must be a modern equivalent somewhere.