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I hear everyone talking about bags as we approach Guild Wars 2's three day head start. Most of the people toting that bags will be the biggest money makers in the game are World of Warcraft players. In WoW, bags are the easiest way to make consistent gold for crafters. The materials are rare for the middle of the road bags, since so few players are farming mobs that drop them. This leads to a situation where low level bags are actually worth significantly more than they "should" be according to their size and the size of the largest bags.
In Guild Wars 2, however, crafting bags will actually level your character. If your character can make a bag, then odds are they will while leveling as the bags seem to have really cheap materials. Initially, bags may not be huge money makers due to everyone having easy access to the materials and the fact that there's every incentive to make and use your own bags at first.
I predict that you will be able to make 4-10x as much selling bags months AFTER the initial rush to level 80. So as an opening strategy, you may want to actually buy bags and materials with whatever gold you make initially from selling them. Just keep reinvesting and stockpiling mountains of mid level materials and bags. That way you will have the WoW situation months later where bags are super valuable and the materials required to make them are scarce/valuable as well.
Keep in mind that you can very quickly turn materials into bags, so stockpile the materials wherever possible instead of just crafting tons of bags. This will enable you to sell off materials if that's more profitable as well.