Bring Towels (Yes, Plural)
I showed up to a C1.5 class, the level between the introductory C1 and experienced C2, without a towel to cover my mat and was quite literally a hot mess. I had read that the C1 classes were unheated and that C2 classes were very hot — up to 100 degrees and with added humidity. For some reason, I assumed C1.5 would also be unheated (a ridiculous oversight on my part) and spent the entire class sweating and sliding around on my mat. Always bring a yoga or bath towel to lay over your mat, no matter what level or style of class you're going to. The rooms remain hot after each class even if it's unheated, and the classes are almost always packed, making it even hotter.
Bringing a hand towel to keep by your water bottle is also a good idea. I did not do that for my first class and during downward dog, gravity pushed a bead of sweat into my eye and, let me tell you, that stings. As the class went on, I noticed some people had small towels with them and would periodically wipe their hands or face with them. Next time, I made sure I brought one, too. If you're planning on hitting the showers afterwards, bring a third towel and leave it in your locker.