(Edit: I bring to your attention Breevok's comment below)
The Cataclysm crafting water element. Yes. Now.
During a gold rush, you make gold by selling shovels. Water Walking was that shovel.
A guild mate saw something I didn't know about. For a very brief window you could farm Volatile Water. Not useful for anything now, but an incredibly valuable head start to any server first profession toons.
He asked that I keep it quiet and not blog about it. In order to both honour that request, but still to get a 'scoop', I did the next best thing. I advised readers to make Water Walking elixirs and fishing aids.
The trick (now fixed) was you needed to be between Wetlands and Arathi Highlands, walking on water and fishing.
So, if you want a head start on those professions, have a look at your AH. There just might be volatile water or Cata fish. Be warned - there is not much supply, and should be priced accordingly. (Yes I do have a limited supply)
If you are after that professional server first, you will need every bit of assistance you can get.