Questions Regarding Half-Ironman Aid Stations

No different than shorter races in most cases.

They usually have water and sometimes pre-made bottles of whatever sponsored sports drink they are using (or straight up Gatorade bottles in those events sponsored by Gatorade).

Volunteer holds it, you slow down, they extend out and try to run with you, you take it, put it in your cage or just dump it right into your aero drink thingy.

Each race may vary a little with what they will carry, but the basic gist is the same.

Exactly, so you don't want to start with your best/favorite bottles, as you're unlikely to get them back. 

Go get one or two of the 24-oz Gatorades in the "bike bottle" form and test them on a training ride. 

heh, I did that my first HIM.  I had to chuck one of my favorites!  Not that big of a deal though.  I collected about 4 new ones from that race.  It's funny how the problem never occured to me untill I was riding up to the first station, thinking "eh, what am I going to do?  I need new bottles, but I don't have any spots!"  Saw the empties in the ditch, and "ding!" light went off and I started chucking...

I chuck every thing on the bike just before getting to the station (in the designated area - OR if the area is not indicated, I waited till I saw a pile of spent bottles on the side and added mine to them).  Even if they were half full - I would toss them for a full, and COLDER, bottle...

Depending on when the first aid station is you might be able to start with just one bottle or even a half bottle.  The lighter you are, the faster you go.  You could take only what you need to get to the first water station.

Of course, the risk is that something will go wrong and you won't get anything at the aid station, but that risk is pretty low.