Check the warranty. If the warranty is still valid and can be used anywhere in the world, then getting a replacement in case the laptop breaks is easy. If the warranty is not global, buy insurance.
Buy an international electric adapter. Greece uses two types of electric connectors: The Northern European three-pin version, and the Southern European narrow two-pin. Most international airports have universal electric adapters for sale.
Pass airport security. Laptops have to be taken out of their cases, unless the case is a new "laptop-friendly" case which can be X-rayed. If the security alert level is high, it is possible that you will be asked to switch on the laptop. Keep the batteries charged.
Use public Wi-Fi. The Greek government is investing in public Wi-Fi hotspots all over the country, to make access open and easy to the general population. So far, however, the public access is only available in a few cities. Hotels may provide free access, but often prefer to charge for it.
Alternatively, use wireless broadband. Mobile operator Wind offers a "pay as you go" subscription, provided you have your own mobile broadband module, or buy one at the same time as the subscription. It is more convenient than Wi-Fi, because it is literally available almost everywhere, but it costs money.
Alternatively, use wired Internet. Some hotels offer wired broadband for free, as do some Internet cafes. Dial-up Internet access is still common, but expensive. In areas without Wi-Fi, that may be the only option, if you do not use mobile broadband. It is likely to be rather expensive.
Make a habit of securing the laptop already in the airport. While theft is no more common in Greece than anywhere else, it still makes sense to lock the laptop whenever it is not used.
