[rslomkow]

1) Packing your lungs is over-inhaling. If you are not Scuba diving or doing it too often it is not too dangerous (*maybe* somebody will correct me)

a) breath in full to using the diaphram (belly breathing)
b) keep breathing in filling the chest
c) use a fast inhale
c) repeat (1 or 2 times is probably safe)

you may find it easier if you roll your shoulders back or you lean bend backwards a little while doing the inhalation. If you keep doing it for too long you waste more o2 than you gain. My understanding here is the if you over-force yourself you can strain your lung and you have no nerves so you won't feel it.

2) most modern freedivers do not advocate hyperventilating. The problem is that you can actually reduce your O2 capacity in your bloodstream. You do increase your CO2 tolerance because you empty your lungs and have less urge to breath. training breath-holds aka tables can increase your C02 tolerance in general without doing the hyperventilate. Most people do find 3-4 deep breaths do help with increased oxygenation of the blood.

3) caffiene absolutely reduces your breath holding time. It increases you pulse rate, every time your heart beats you consume a more oxygen. If you really want to stay down longer you have to lower your heart rate.

I have heard the same for alcohol, I assume it is because it increase blood pressure.

As covert mentions it is a mind game. You have to teach you body both how to relax and work at the same time, you have to relax all the muscles you are not using. Also a large part is psycological of learning when you really need air and when you body is just complaining. Practice helps, it lets you know your limits and extend them.

Good luck!