The meat on a stick is chicken and they wrap it in a pita type bread and then you get various veggies thrown in with some sauce. These carts have sprung up all over the place in the last few years in Thailand. You can find them about every 100 meters now. There is a trick to doner buying and that is buying it at the optimal time. Do not get it when the stand first opens and do not get it late at night no matter how hungry you are. That meat has been sitting there and getting further away from the heater as the day goes on. Optimal time is between 8 and 10 PM. Last trip to Thailand my second round of food poisoning was a 1 AM doner and boom, I was down again. They are tasty, just make sure you follow the time rules.