Hmmm 
Human in Classic times.
Yeah that’s a given, since I already know how things are going to work out.
The people of Stormwind would throw me in the Stockades for sounding like a lunatic!
Seeing as I’d have no powers though, no abilities besides what I can actually do in real life… some of the random stuff that’s come into my head while reading this thread:
I’d find a pin and go stab Katrana Prestor in the tush to see if she turns into a dragon.
Or I’d become some kind of Nostradamus type figure writing prophesies of the future.
Maybe play the Auction House a little if I can find some way to earn some silver (picking flowers as others suggested seems a good start)
Befriend a Mage and see if we can work out some way to get in touch with Rhonin and Khadgar (without collecting several thousand of some random thing he wants)
Tell Bolvar never to go to Northrend, ow and let him know where Varian is.
Go sightseeing… I’m in Azeroth, I’d tour the city, “borrow” a horse, see Elywnn Forest and Westfall for real.
Try to figure out what my natural aggro range is against some very very low level, possibly already wounded creature or NPC.