Wow - all that caffine! Coffee, tea and smokes work while your young, however after 20 years of doing that you'll add an extra 10 years to your body's age. If you want to look good after your 40, STOP USING CAFFINE & SMOKES TO STAY ALERT!!!
Computer workers are prone to mental fatigue, not physical. Mental fatigue is countered best with 3 methods; glucose, exercise and sleep/rest.
Glucose: Because your working with your brain, it demands a constant flow of fuel - glucose. If your body runs out of glucose, it will draw upon reserves in the liver to compensate until you eat again. So keep up the carbs throughout the day (not sugar because it requires energy to break down into simpler carbs before the body can use it). Personally, I buy glucose syrup and add it to green tea (low cafine) and I drink 4-6 cups a day.
Exercise: Not a 5 mile run or a gym workout. Take a walk around the block instead of having a smoke/coffee. Get a 10min stretch routine that engages the larger muscles of the body; this will up your heart rate. After a 10min walk around the block, or a proper stretch routine, you'll feel more recharged than with a qwik coffee.
Sleep (naps): Take an afternoon nap! A billion people can't be wrong. In many cultures, an afternoon nap is a given. Even if you're only able to lie down for 20mins, this is enough time to lower the heart rate and give your brain a rest. Try to let your mind wonder, not chew over work problems.
All that bloody caffine and smoking!! Youth is wasted on the young I tell you. Look after yourselves for christ sake.