One Ringy Dingy
If you have to dial to reach an ISP, check to see whether yours offers local numbers in exotic locales, or the long-distance charges as you transmit your opus to eager literary agents will kill you.
Look up those local numbers before you gooften they're only available online, which is singularly useless if you can't get online to find them!
If your computer has been gracedor afflictedwith Microsoft Office, have you run each of the applications in disconnected mode to make sure it has all of the bits it wants? Few things are more irritating than being asked for installation media that's on a network 1,500 miles away, when you try to use a feature that some genius decided should be set to "Install on First Use."
Okay, the computing needs have been satisfied. Now turn your attention to slightly lower-tech: your faithful cell phone. Does your carrier have a roaming agreement with the telco-by-the-sea? If not, you might as well stuff the handset into a drawer at home and rent a compatible phone. Ditto for your faithful BlackBerrywhy carry it if it's just going to be a paperweight?
If you're lucky enough to be sure of dial tone in paradise, don't forget the phone's charger!
PDAs, on the other hand, can be useful even without connectivity. Again, make sure that the contraption has been backed up in some way. Pack extra batteries, or the cradle and charger (you can buy a cradle-less synch cable and charger to save bulk).
If the unit has never been synched to your laptop, better do so at least once before you leave home.