Although its a little early to say anything definitively until they released beta information, it's likely, as with every new expansion, gold will probably be at least twice as common as the previous expansion. That means that any gold you don't spend in the first week or two will probably be devalued to half its current buying power.
Now is the time to stock up on goods that you feel will increase in value and diversify your wealth. Rare pets and mounts (bikes and vials aren't going to get any cheaper to make), crucial crafting mats and anything that would appeal to a tsunami of baby pandarians. While most players will create leather-wearing monks, about 20% of players will no doubt make pandapriests and panamages and whatever other classes the race can take.
Nowadays people level their baby toons so fast that I wouldn't worry about low-med flasks or elixers or gear. Most will be using heirloom gear so any appropriate enchants should sell well. (So stock up on the enchanting mats now.)
Another area to look at right now is the transmogging market. I see a lot of otherwise useless gear going for some helfty amounts of gold due only to how they look on a character. Check out http://www.wowroleplaygear.com
for a place to start your shopping list.