Call it what you want, it's a container of sorts made of a soft material that you tie a strap to and put over your shoulder. I started carrying one on a daily basis starting in grade 12 around 2002-ish. Ah, that was the great year of experimentation...
While I went to a school for nerds where a sense of fashion was non-existant (you have no idea...), men and purses were still not a very common pairing at the time. Inspiration probably came from one of the cool kids who wore one to school in place of a backpack all the way back in fourth grade.
Nowadays, a guy wearing a murse is a pretty common sight - that or I finally started to pay attention. These are your future customers if you're a chiropractor. I'm going to get right down to it: wearing a shoulder bag sucks if you actually have anything to carry. This pendulum on a string doesn't stay still, it will hit your ass and thigh non-stop when you're walking, you will slouch to one side to compensate for the weight, and your shoulder will ache and pain when you're on your foot for too long.
Don't get me wrong, there are ways to compensate for some of those cons. You could shorten the strap so that it looks like a lady's purse, and then swing it across your chest so that it hangs half-way up your back. Congratulations, you've now created a single strap backpack that constricts your breathing! Or, you could lighten the load to save your back and shoulder, making it as useful as a wallet. And then there's the pendulum thing: I find that you need your bag to be a certain weight to keep it steady while walking. Not too heavy, but heavy enough - you'll know it when you feel it. Me? I end up holding my bag still with my right hand most of the time.
Enough complaining about the bag. I choose to carry one for the majority of the year no matter how much I shit myself for it. So, what does a "dude" (i.e. me) look for in a bag?
For the ultra functional common "dude", one does not cycle through purses from season to season. Almost a decade later, I have only swapped through four different purses. And each swap was out of a sense of function, comfort, and okay, some style.
Price is also not that important, by which I mean it doesn't have to be fancy or branded. My first bag came from a popular outdoor's equipment store, the next two from army surplus', and my current one, I stumbled across at a bookstore. All but the first were cotton canvas, and all less than $40.
How does that help you? It doesn't, which is why I, with nearly a decade of man purse experience (bad ass credentials), will go through some pointers.
As far as I know, men don't really brag about their bags, or use them as status symbols. If you're metro and a hardcore fashionista, then it's been nice knowing you. Bland and functional is where it's at. Think Jack Bauer's go-to armoury (Google search terms: "jack bauer purse"). That is THE model man purse. What could be better than a container filled with guns and explosives carried around by the epitomy of an alpha-male going around killing people?
The most common materials that I've seen are cotton canvas, leather, and nylon. I would stay away from nylon no matter the cost or style because it just seems "cheap". No matter how water resistant and functional, it screams Targus laptop bag.
Leather and cotton canvas are excellent choices as both should be somewhat rain resistant and wear-resistant. Another benefit of cotton canvas is that it can be patched easily with a needle and thread. With leather, it may be a more difficult to do simple patching work, and maintenance is a bit more intensive; it makes up for it in durability though. On the aesthetic front, leather is definitely "prettier" and fancy schmancy depending on the colour and "pattern". Be careful with black leather: it's much more formal and harder to get right.
Size is also another biggie. You should be able to fit a letter-sized page in a landscape orientation into your bag (get a clipboard). Anything smaller and you're crossing into fanny pack or lady's purse territory. Too big and you should just get a duffle bag, which isn't that bad for anything other than your back (and your frightened coworkers). Preferably, the overall shape is a rectangle that is longer horizontally than it is vertically.
Here are names of some awesome shoulder bags that I love (google them because links to specific products at stores change too often) and links to stores that sell some not too shabby bags. They are also stupidly expensive, so find something you like and then search for something cheaper if you want. Go forth and find your purse!
Ideas:
Belstaff Colonial Shoulder Bag
JCrew Bags
Roots Canada Leather Bags
P.S. Seriously, think about just using your pockets if you can manage it. I've grown sick of carrying my bag and wish I didn't have to. But obviously, having a couple liters of storage space on my person is pretty convenient. Also, think about getting a leather binder with a zipper seal. That's been my go-to container in the winter when I usually have enough pockets to get by.