Katara - some waterbending
In response to Sokka and Katara at the Air Temple thing: I always thought that traveling on Appa helped them adjust to higher altitudes. Also we don't really get to see their journey from the southern water tribe to the southern air temple. So we don't have a great time line for how long it took to get there. While I agree that they were a little too well adjusted, I think a couple weeks of flying at high altitudes with Appa would have definitely helped them adjust to the Air Temples.