One of the most problematic aspects of the avocado is that it turns brown quickly due to oxidation. Although it might not be spoiled, the off-color makes it look unappealing and unappetizing. The way you store avocado can make a big difference in how long an unused avocado stays fresh and green.
I usually have no problem eating an entire avocado whole, but I know most people prefer to eat in smaller portions. The high fat content of avocado means that it packs quite a caloric punch, so is prudent for most people to eat only a half, or even smaller portion of an avocado per day.
There is a great kitchen tool called an avocado saver that is perfect for storing the unused half of an avocado. It is molded in the shape of a half avocado with the pit removed. What you do is slide it over the other half of the avocado and it fits perfectly, preventing contact with air. This keeps the avocado from turning brown better than putting it in a sealed container or wrapping it in cellophane.
It is best to store cut or peeled avocado in the refrigerator to preserve freshness and prevent browning. If you place the avocado in an avocado saver, you can take it directly from the refrigerator and put it into your lunch bag. It is perfect for bringing avocado to work or school for lunchtime snack.
In lieu of an avocado saver, the best thing you can do to keep avocado green and fresh looking is to drizzle fresh lime or lemon juice on the exposed flesh of the fruit. The high acidity level of the juice prevents and slows the oxidation process.