The Getaway, Book 12 by Jeff Kinney

Greg Heffley and his family are getting out of town. With the cold weather and the stress of the approaching holiday season, the Heffleys decide to escape to a tropical island resort for some much-needed rest and relaxation. A few days in paradise should do wonders for Greg and his frazzled family. But the Heffleys soon discover that paradise isn't everything it's cracked up to be. Sun poisoning, stomach troubles, and venomous critters all threaten to ruin the family's vacation. Can their trip be saved, or will this island getaway end in disaster?