(Book tours 2 is right below this post.)
I just remembered another important point, which is that even when publishers pay for a book tour, that tour may still be expensive--sometimes frighteningly and unexpectedly so--for the author. There have been a couple of times when I had to think seriously about whether or not I could afford to do a tour even though my publisher would pay for it.
Some authors are presented with a corporate credit card, which is ideal. I've never had that, and I suspect most of us don't. If you aren't given a card with a preset limit, you will be told to pay for some expenses out of your own pocket and then bill the publisher afterward. This is not a good thing for writers who are not rich! I've had to pay for. . .shuttle to and from KCI, which with tip is about $40 or so each way; meals outside of the hotels; airport parking for my own car; taxi fares--which can be $50 or more if you have to take them to or from airports, for instance. In fact, count on paying for every taxi ride out of your own pocket, and be sure to get that receipt. Also make a note every time you pay a bellman or a hotel maid. (You do leave tips for hotel maids, don't you? Of course you do.) If you eat outside of the hotel, you will pay for it, so get those receipts, too. (I've gotten around that by eating only in hotels, which works as long as the hotel restaurant is open.) There are other expenses for which you will not be reimbursed--such as, for instance, anything you need to buy in order to do the tour--a new outfit, for instance, a haircut, new shoes, clothes for going to places where the weather is far different from yours at home, etc. If you have pets, there will be that expense. You may have extra childcare expenses. The last time I went on a national tour I had to pay for two weeks care for two dogs and two cats. Expensive! This is no big deal if your bank account is heavy with cash, but how many writers--especially those with no outside source of income-- have that much elastic in their budgets?
What I'd advise is that if you can possibly budget in advance, that would be a good idea. It's scary to be confronted by a call for your credit card when you may not have enough to cover the bill, or to suddenly need to take a taxi when you didn't expect it
What expenses have I forgotten?