I have used large external batteries to keep my notebook going before. The downside is that that things tend to be heavy and often won't work for a wide range of devices.
A new solar batter from Chinavision has turned up that sells for $148. The thing is very large and packs in a battery holding 20,000mAh of juice. The beast has 29 different adapters that lets it work with all kinds of notebooks, cameras, and phones.
The battery can be charged fully in three hours from an AC outlet or in about ten hours using the integrated solar panel. That means you can set the thing outside for a full day and power your notebook for a long time.