Suitable clothing for wildlife photography should be practical and comfortable. You should also preferably stay away from bright colours as this may discourage wildlife staying close. Long sleeves on bright days, even in winter will prevent sunburn as will a hat. Insect repellent is also a must in the warmer summer months and particularly when shooting in the evening where mosquito borne disease is prevalent. 
Solid shoes are a must, and studded rock boots are a good idea when shooting on our Central Coast rock platforms. Nobody wants to see broken Camera gear at best or worse personal injury.
The weather can change quickly so make sure you have a coat in the car just in case the weather turns bad!
Clothes are made for your camera and lenses also. Raincoat branded lens covers protect your gear when the weather gets nasty.