[Advocacy] What sizes will be needed for blog banner, t-shirts, etc?

[Ivo Emanuel Gonçalves]

I'm supposed to contact Sebastian Kraft and Mike Brooks to request
that they create t-shirts, flyers, banners, blog stuff, buttons, etc.
They agreed to do this some time ago and will probably still do it.

But I have no idea what exactly are we going to need or what sizes to
use...  While we do have the SVG files and probably could adjust as
needed, I would rather enlist the help of the experts themselves.

So, can anyone suggest ideas for a big list of what we need and
respective dimension sizes?

-Ivo