Know any good messenger bag posture tips? I've just gotten my hands on this, and I need to put heavy-ass textbooks and my laptop and charger and exercise books and useless crap inside it, and I'm wondering how will it affect my back. I'm in average shape (eg. not fat), but I'm not so sure about the stress it will put. Anyone else use messenger bags with these sort of experiences, I'd love to hear it.

Is that what they call those bags these days? I always thought they were record bags. And although I've been using such bags for years, I've never bothered putting a laptop in one.
But having said that, the way you'll wear it is no different really to the old Dell Laptop carry cases, and if those are anything to go by, the strain will depend really on the weight of your laptop and anything else you put in it.
I know that my laptop used to cause the carry case to dig into my flesh after long periods of continuous use, but this was a decade ago and I expect laptops are a fair bit lighter now.

Well, I never really used those laptop bags that came with the computer anyway (because I didn't want a mugger to know I bought IBM), so I don't really know much about this. I carried laptops with sleeves and I'd just hold them around.

I use a bag that's worn the same way (though look different), and having to much crap in it makes my back hurt immensely. If you have a lot of heavy stuff to carry, I would recommend getting a proper backpack instead.

Don't carry anything above 3-4 kgs in a one-shoulder bag for any length of time, it'll strain your back beyond the point of healthy excercise.
If you plan to carry a 3 kg laptop + 3 kgs of books + various things, get a backpack that you carry the standard way, with both shoulders.
I remember back when I was in primary school it was the "custom" to always carry your backpack over one shoulder, even if it was designed for two and was full of books. You'd have a slight backpain after just a few minutes of this if it was heavy.

Yeah, during Yr11-12, I was lugging around 20 kilos (at least) in a big camper/vacation/sports bag due to the amount of books and material I had to carry. Did my back no favours, but with not much in the way of lockers (and being the kid they picked on, it would only end up with chocolate milk inside) and the gauntlet in terms of subjects I had no real option.
You want a sturdy bag, that can be worn over both shoulders, and keep a good walking posture. Don't slouch, especially if you have a day with a lot of extra weight in it. Try to keep only the minimal requirements inside, if you don't need it for the day/class leave it in storage or at home.

Yeah messenger bags are for girly people, you want a big manly backpack that looks cool and that you can carry a midget in for emergencies.
I used to lug much the same 20kg of books to school that Ois did but when I had English & we were doing shakespeare I didn't like the lame little book we had for Henry V so I lugged the globe illustrated shakespeare as well
Of course my back is fucked so you might want to take my advice with a grain of salt.

That's so... crazy?

I choose to interpret that as astonished admiration at my sheer level of awesome underplayed with a hint of sexual desire.
I hate to tell you but we can never be more than just good friends...

And if you really want to make sure you keep injury free ... get a backpack like this one. Your hips are able to take loads and loads of weight. Your shoulders aren't.

As others have also mentioned, those bags really aren't suited for carrying any kind of serious weight. They're nice if you're just lugging around a few light books, some papers, maybe a light laptop, but anything more and you should get a proper backpack, otherwise the uneven weight distribution will start giving you shoulder and back pains in no time. The fact that the bag you linked to doesn't have any kind of padding on the shoulder strap will also give you the added joy of the strap digging into your shoulder when there's any kind of significant weight in the bag. So if you really do need to carry around all those things you listed, do your shoulders and back a favor, ditch the bag, and get a backpack.

Or get a netbook, they're relatively cheap given their capabilities and are good for office type tasks whilst weighing around 1KG.
Also as a side note, they seem to impress girls. I've had quite a lot of "Ooh what a fancy little laptop" conversations since I got mine

Wow. Wow. Wow. Wow. Wow.
I don't know what made me buy the Kremlin from , except maybe the fact that it's about the size of a freaking space shuttle. Maybe I'll get into that bike commuting thing or something, but that bag is waaay too big to carry around on a day to day basis. So I'm getting a [url=http://www.chromebagsstore.com/messenger-bags-mini-metro.html]smaller variant that is still bigger than the biggest Timbuk2 bag.

In the UK they are known as 'ManBags'. Very popular in Brighton.

They're about as manly as a cosmopolitan cocktail.