The Long Haul (Diary of a Wimpy Kid Series #9) by Jeff Kinney

A family road trip is supposed to be a lot of fun unless, of course, you're the Heffleys. The journey starts off full of promise, then quickly takes several wrong turns. Gas station bathrooms, crazed seagulls, a fender bender, and a runaway pig-not exactly Greg Heffley's idea of a good time. But even the worst road trip can turn into an adventure-and this is one the Heffleys won't soon forget.