As you've probably noticed via the blog I read a lot; technical, fiction, and non-fiction. Reading can be an expensive habit. I definitely buy a few books during the year, but especially for vacations I've found it useful to supplement by budget with a visit to my local library (I typically go every 2 weeks anyway). Nice to read the just released stuff without paying full price, and I can grab a couple extras just in case. For close to home vacations carrying a few pounds of books is well worth the work.
For travelling though, I have enough stuff to carry without a bunch of hard cover books. The main branch of our library also has a used book store, ranging from .50-$1 for both soft and hard cover books. I'll generally buy a handful, some of which may make the round trip, others that I'll leave behind at the hotel for the next visitor to peruse.
My friend Steve Jones recently purchased a Kindle which I guess eliiminates the weight/bulk factor, but doesn't do much for the budget unless you read the few free books out there. Not a bad solution, just seems overly expensive compared to my low tech approach. Sometimes analog works just fine, and since we've already printed the book, getting one or two more reads out of the paper doesn't seem like a bad deal at all.