This will largely depend on the type of air fryer you have and what accessories are available.  Some accessories are pretty good such as double decker racks, pans, etc.  I would definately recommend getting the following two things though.

• Spray bottle for oil (only required on some foods if there is no oil in the food.
• Instant digital meat thermometer – This is a must if you intend on cooking whole chickens or any really thick piece of meat.  Some foods are more important than others, but if you are cooking something like a chicken, you want to ensure the meat is properly cooked in places such as under the thigh.  I recommend a Thermopop personally as I have one.  It takes only a couple of seconds to tell you the temperature, and is very accurate.  Unfortunately, they aren’t cheap, but good quality rarely is. Here’s an Amazon link to a Thermopop in case you’re interested in having a look.