I have no experience with the 2xTC, but I hear is will degrade your AF speed quite a bit, so you may want to leave that in the bag.
Not so sure about that. 70-200 on a 5D Mark III does not give you much reach, and unless the planes are static they are likely to be some distance away, especially during flight.
The 1.4 is definitely preferable to the 2, but it may be an idea to see if you can rent a longer lens for the day.
I also agree with everyone about leaving the tripod at home. At most air shows you will need to be very flexible!