Zombie John Marston.
The Hat
You can't be John Marston, reformed outlaw of the American frontier, for Halloween without the right hat. This distinct crown is a Marston trademark, The Packer. You might want to rough it up a little, and add a feather to that bad boy.
The Vest
You have to have the black denim vest. Your best bet would be to grab a dark denim jacket and cut the sleeves off about 2 inches from the shoulder. You can find some affordably priced ones here.
The Shirt
Make sure your sleeves are rolled up so others know you're ready for super duty tough work on the plains. Chances are you'll run into a zombie or two while you're out that night anyway - best be prepared for action.
The Gloves
It's rough out there - protect those mitts with a nicely worn pair of goatskin gloves. You should be able to find a comparably affordable pair at any western wear or even big chain store near you.
The Satchel
Carry your treasure maps, holy water, and looted peanut chews in an all leather sling bag. Only for the premium Marston costumer.
The Pants
Pleats and pinstripes. You might have thought that John Marston was wearing denim throughout his adventures on the frontier, but upon closer inspection you'll notice they're actually pinstriped bootcut pants. Denim wasn't quite so sophisticated back in the early 1900's.
The Belt, The Buckle, The Bandoleer and The Holster
A cowhide belt with a buckle big enough to be a Spartan shield and a holster will really tie the whole look together. And plenty of costume shops have acceptable looking rifle bandoleers in stock.
The Boots
Oh yeah, make sure not to forget your boots and spurs. Some non-descript boots will work in a pinch, just don't play yourself wearing some Air Force Ones with your John Marston get-up.
Undead Bonus
As mentioned earlier, you can give the whole ensemble a Nightmare-ish spin with a good zombie mask - that one is on the high end but comes complete with eye-socket worms.
