There’s an app for that!

If you have an iPhone, or possibly this is available for other PDAs, you can get a free app called Lose It!
This app can keep track of everything you eat, plus record any exercise you get and help you keep track of the calories you have eaten so that you don’t have to keep a journal with you at all times. I was basically doing this on an Excel spreadsheet, but of course couldn’t record anything until I got home. Now I have this information with me all the time.

An added benefit is that you can look up the calorie content in any foods purchased at the grocery store, and choose a portion size and it adds the calories to your list for you. I just ate an apple. I made sure I measured the diameter, which was about 3 inches, and found that it had about 95 calories, so I chose to add it to my list for the day under snacks. It’s a really awesome tool to help you lose weight!