> <initializer_list> is "built-in"

You still need to include the header for any of the following:

1. Constructors (or functions) with `initializer_list` parameters.

  template<typename T> struct S {
          vector<T> vec;

          S(initializer_list<T> il)
                  : vec(il) {}
  };

2. `initializer_list` literals in range-for loops.[1]

  for (int prime : {2, 3, 5, 7, 11})
           // ...

3. Named `initializer_list` variables.

  const auto primes = {2, 3, 5, 7, 11};
  const initializer_list<int> primes2 =
          {13, 17, 19, 23, 29};

> <iterator> is generally subsumed by "auto" and type inference.

The iterator adapters[2] are still pretty useful and (I thought?) commonly used.

Also, the "range access" and (new for C++17) "container access" free functions are very useful for writing template code that works with both C arrays and STL-style containers, but they're defined in many other headers.

[1] Useful with variadic templates:

  [](auto&&... args) {
          for (auto &&arg : {args...})
                  // ...
  }

[2] http://en.cppreference.com/w/cpp/iterator#Iterator_adaptors