Staying in sync without a cloud

The wife and I are in Mexico and will generally be somewhere between here and Tierra del Fuego for the next few years. When we housesit we will normally have good wifi, but in-between our data access will be sparse. We have two MacBook Airs and two iPods and I'm trying to discover the best way to keep our calendars and contacts in sync without requiring 24/7 internet access to a cloud service. This means that Dropbox and iCloud are not ideal solutions. Just wondering if anyone else is now or has been in the past in this type of situation, and how you dealt with such issues? I would love to hear your creative solutions...