We are operating on the assumption that hammer space does not exist in Warcraft, so your character will only have what they reasonably could have had on then at the time the Burning Legion crossed into their timeline. That's things like armor, trinkets, maybe a toy or two -- anything that would have portaled them somewhere (like Jaina's locket) will not function. Anything in your bank or void storage will not be brought with you.

The key thing is that we are using the setting more than actual game mechanics. So, for example, your Deathbringer's Will isn't going to transform you into various creatures when you use it.

Non-combat pets and mounts will not arrive with your character (no dreadsteeds, deathchargers, or paladin chargers), nor will any extra gear, and flight masters and such do not exist here since we are sitting in ancient Kalimdor. Your characters are welcome to try and set up forms of convenient transportation if they ever make friends with neighboring species like the night elf villages.

Mailboxes do not exist. HOWEVER crude ink, quill and parchment is the major form of communication here -- so if a character was interested in trying to circumvent the faction divide that way, its totally possible, but they would have to be sneaky about it. Maybe tame some wildlife into playing carrier pigeon. ;)

If there is anything I missed, feel free to ask again!