In an effort to give people an idea of some of the extra equipment and costs (in AUD) of getting setup with an airbrush I've made a quick tally of some of the extras that I have purchased. Like many tools none are essential but most make things easier. For pretty much all of them I would recommend eBay as a source of supply, especially on the disposable items.
* Glass cleaning pot - $15-20
When cleaning out your airbrush between colours you need to spray some cleaner/water/etc through it. Rather than spary that into the air and contaminate the piece you are working on you instead spray into this heavy glass pot. The lid has a filter on it so the paint/cleaner stays inside. The pot also doubles as an airbrush holder. Recommended.
* Cleaning brushes - $5
Usually sold as a set of different sizes these are small brushes to clean out your airbrush. I don't use mine much now that I use q-tips, an old toothbrush and paint brush instead.
* Disposable mixing pots - $2 for 40
The clear plastic shot glasses sold in grocery stores make great mix pots.
* Q-tips (ie the things you clean your ears with)
I find these very good for cleaning out the paint cup and needle of my dual action airbrush. They absorb the last traces of paint that always seems to be left in the bottom of the paint cup. Buy decent ones as the cheap ones come apart and leave bits behind which will block up the airbrush nozzle. Yes, this is the voice of bitter experience.
* Quick connector - $2-3
Handy as you can disconnect your airbrush without draining your air tank. That way you can do a full clean or swap airbrushes. For a dollar or two more you can get ones with a small screw dial that limits the air flow too.
* Plastic pipettes - $2-3 for 20
Great for mixing and adding water/thinner/etc into the paint cup. At art stores I saw them for $1 each, so another item where ebay is the winner.
* Airbrush holder - $10-15
These have mounts for both normal gravity feed dual action airbrushes and other types with side cups. Now that I have the glass spray pot I don't use this anymore except when I'm using my Paasche Model H. Some models clamp onto a bench, others are free standing.
* Needle oil - $5
If you are going to buy a decent airbrush, best to look after it. A drop or two of oil every few sessions is all that is needed.