Awhile back I was also compiling some basics along the lines you are looking for, and some of the things not already mentioned that I was including were:
1). Types of the fundamental representations (real, complex, or quaternionic)
2). Simple relationships between the fundamental representations (in terms of exterior powers of extremal fundamental representations based on a result of Adams)
3). Adding to the listing of maximal subgroups, the decomposition of fundamental representations on restriction to a maximal subgroup
4). For lack of a better term, "Quotient of Faithfulness" indicating for each fundamental representation what quotient of the simply-connected group the representation is a faithful representation of; this information is useful for questions of distinguishing between actions such as $Spin(k)$ vs. $SO(k)$ and determining whether a given reducible representation of $Spin(4n)$ is faithful (since it has no faithful irreducibles).
I also had a few other little facts that aren't widely known or used but that I was using in my research. My version was going to be in the form of a short pamphlet, but I definitely think a nicely layed-out poster would definitely be very cool and useful.