Between the first and second finger of my off hand like a cigar. 
Ian
If I am expecting a second shot, I also do this. I also like the two round wrist holders for the summer chucks and song dogs. For general hunting 2-3 rounds in various pockets works fine.
I have never had a need for an instaneous second shot.
I wish I had a video of it, but some 5 years back my buddie and I took our wives on one of those canned boar hunts. We would video, they would shoot. Don't you know the week end was a rain out. Temps where in the low 30's and it was a rain/snow mix. the girls elected to stay in camp. We figured, its paid for and we are already here, so, we headed out. Now, I had only brought an old short barreled Handi 12ga with peep sites and a hand full of buck shot and two slugs. Figured I would only need it for finishing a wounded boar off or fending one off a mean one.
The guides figured they would try for to really big ornery boars known to be on the back side of the property in a thick swamp. We slowly walked along a hog trail, when the guide in front of me stops and slowly backs up. As he stops beside me he says there is your boar, right there 30 yards out just to the side of the trail. Just then he lets out a snort and gets up running straight at us. As calmly as I can I shoulder the handi, center the front site on his head as near as I can tell between his eyes and squeeze the trigger. BOOM, the pis literally skids to a halt some ten feet from us. Well I THOUGHT, we where all there. More on that in a moment. Just as quick as that, a second pig jumps up and he charges too. I have already got the handi open and had just inserted a second and last rem slug. This time the boar stops after only going a couple feet. My buddie is yelling he has no shot. The pig turns to walk away, but pauses and looks back. As if to say, "Your still here". He instantly spins and is barreling down on me. All the time my buddie from somewhere behind and to my side is yelling NO SHOT, NO SHOT. I shoulder the handi and repeat what just happened seconds before... BOOM, the second pig LITERALLY dies on top of teh first pig. Both with a 1oz slug in the noggin.
There I am, standing in a couple inches of mud and water. Still smoking Handi in hand with water streaming off my cowboy hat. I look around to see my buddie walking toward me, with a huge smile on his face. The guides are NOWHERE TO BE SEEN!!! In a couple seconds they emerge from the brush running up to us, hooting, hollering and smacking me on the back. Both couldn't believe what they just saw and just had to see this little gun. They couldn't believe how I just stood there, coolly loading the gun as the pig charged me. Then boom, one down and a couple seconds later, boom second pig. Both where solid 300Lb pigs.
SO, with some practice and a cool head, loading for a second shot, in a single shot, ain't no big thing. I just wish we had been able to film that...
CW