1. Enable LaTeX input mode: C-\ "TeX" RETURN
2. Typing \Bbb{R} should now result in ℝ,
   but (for example) \Bbb{C} does not result in ℂ.

I miss at least ℂ (field of complex numbers), 𝔽 (generic field), 𝕂
(generic field, German), ℍ (quaternions), 𝕀 (identity map), ℚ (field of
rational numbers), ℤ (ring of integers). Others might miss a few more
that are in common use, see [1].

The attached patch adds all blackboard bold capital characters and "1"
and "2" using the codepoints from the referenced Wikipedia article.

Ansgar

  [1] <https://en.wikipedia.org/wiki/Blackboard_bold>

In GNU Emacs 24.5.1 (x86_64-pc-linux-gnu, GTK+ Version 3.16.4)
 of 2015-06-28 on trouble, modified by Debian
Windowing system distributor `The X.Org Foundation', version 11.0.11701000
System Description:	Debian GNU/Linux testing (stretch)