What to wear for Kayak?

So...it's my first time to do kayak. Should I wear bathing suit underneath the wetsuit or would a shirt and some tight short okay? I am asking because I am in Malaysia now and I did not bring any bathing suit with me and buying one is expensive especially when I am going to use it just once during my stay here. A friend said it's okay to wear just shirt and swimming shorts/trunks but I want to make sure if it is okay...?