As I have said before, I have pretty limited time to play. It is mostly on Weekends and on Wednesday. I usually get a few minutes here and there and like to try and get something done. Here is a small list of things you can do in a very limited amount of time (10-20 minutes).
1) Cooking Daily: If you done have cooking, then you are a damn slacker :) If you do (and you should), pop into Dalaran and do the cooking daily. They are very easy and net you some spice and a dalaran cooking award (or two if you are lucky). It will also grab you 16k XP and a I believe a bit of cash as well. This is time well spent. Beside the Northern Spices (which are needed for making the top foods), you will get some funny parody spices from time to time as well. These include Old Spice (which you put on yourself or somebody to make them smell better) and Baby Spice (shameless Spice Girls reference, but it allows you to shrink people to adorably small sizes. Best used on Gnomes, Bear Droods, and Boomkin).
2) ANY DAILY: If you have any plans on doing any kind of raiding or running of heroics, all of the major rep factions have some nice gear waiting for you. You obviously dont have time for an instance, so go and do a few dailies for your faction of choice. All that rep will add up and you will make a bit of cash to boot.
3) Gather: This one is only convenient if ou logged off somewhere other than Dalaran. An epic flying mount is also prefered. Herbalist or Miner doesnt matter. Get on your mount, fly around the zone and collect your nodes. When you have time to sell them or craft them, it will have been worth it.
4) Fishing: Fising in WoW is nothing like fishing IRL. In real life, you sit there for hours on end, may not catch anything, and (in my case) throw them back. In WoW, you can catch several fish per minute. Catching these fish will level your fishing skill. Leveling your fishing skill means you dont have to do it later. WIN. Also, you can take all of the fish you catch, cook it, and use it for raids or sell it on the auction house.
5) Auctioneer: Play the economy. Log on. Go to an auctioneer. Scan. Alt-tab and enjoy Darraxus the Warrior. Check the auction house for good deals after the scan. Buy then and resell them for more. Profit. This one isnt really incredibly fun, but when you see the cash rolling in, you will thank me.
I hope this is helpfull for all of those WoW fanatics out there who have a very limited amount of time to play like I do.