std::maps. The STL in general is awesome, but std::map is specially great. The possibility of using any type of variable as a key instead of an integer and having random access to the elements through that key looks like magic to me. I have some basic idea of how they work and next year I'll be implementing my own map in class, but right now it looks like witchcraft.
The built-in touples of Python look very comfortable to use, and it could be great to have them. Implementing the swap this way for example:
a,b = b,a;
However, they could be a too big overhead and so inneficient for what C++ is supposed to.
I believe in no gods. I know that the turtle moves, and no false prophet will fool me with their lies. The turtle moves thing is a reference to the book Small gods from Terry Pratchet.