When you are working outside with your laptop, the most important thing that you might consider is to maximize your battery lifetime. This is true especially when you are working on location where AC power is not readily available.
Typical laptop might last from 1.5 hour to 3 hours of normal use. So you might want to squeeze out all the battery juice and put it to good use.
Here are a few tips that I got from surfing the internet to save battery life when you are using Ubuntu (or GNU Linux OS in general) :