I've used vertical and horizontal shoulder holsters. They look cool in the movies but are much less so in real life. That being said... The horizontal shoulder holsters seem to work best when I'm going to be driving for long distances, otherwise in my opinion they are a nuisance because they have a tendency to flop around. Vertical shoulder holsters can restrict your movements and generally require a longer jacket of some kind to keep properly concealed because they can be bulky even for mid-sized guns like the Glock 19. Additionally, offside magazine holders can be a pill to deal with as well if you are trying to maintain a proper stance and control of your firearm. When driving with a horizontal shoulder holster on I'll keep a spare magazine in my jacket pocket on the same side as my shoulder holster for three reasons... first, the weight of the magazine keeps my jacket down helping keep the shoulder holster concealed but helps me sweep my jacket out of the way when drawing, second, I don't have to reach across my body to get to a reload, and third, I've found it faster than the offside mag pouches as the weight of the clip generally does a good job of keeping that pocket in an easy to get to position. I also tend to keep a double mag pouch, either OTW or ITW, positioned on the same side as my weapon holster but slightly to the rear, roughly at the 7 o'clock and the 8 o'clock position. The forwardmost mag pouch has my second reload mag and the rearmost mag pouch is holding either my CRKT M16 or Cold Steel Spartan folder. Both of those folders have the advantage of being easily opened one handed by using a drag draw. Something easily achieved using the offside hand when the mag pouch is carried in that position. I have a friend who liked the way I carried but prefers to reverse it. I normally use the forwardmost offside mag pouch for a nicely sized tac flashlight. He prefers to keep his folder there and an appropriately sized taclight in the rearmost mag pouch on his hip. Either loadout will work perfectly fine if you are going to be driving long distances by yourself. Just remember two things, your holster, reloads, and general loadout are going to be dictated by the situation so think about that situation and assess your option for what will work best for you. Also, make sure you know what laws you are going to be dealing with and plan accordingly. Hope this helped.