In preparation for periods of lack of sleep I recommend meditation over actually 'stocking up' on sleep. The meditation period needs to flow over into the period where you will be low on sleep, as in, you have to keep it up. but 30 minutes of meditation can help you survive an hour or 2 of delayed sleep.
If you cannot do that, when you're feeling tired and sleep deprived 15 minutes of theta entrainment can help, If you meditate you get yourself there if you don't then an entrainment sound track will help. You might continue to feel tired for a few minutes after wards but it's like waking up in the morning. If you don't have entrainment soundtracks try 15 minutes of continuous PhotoReading. Alertness will return and you'll probably find a couple of more hours in you. Then get some real sleep.
Alex
