well I've been thinking about a simple sheet with instructions and templates for a leather and paracord Six hole General purpose sling. The only bit of kit you'd need would be a hole punch - and most poundstores sell those.
That could just be downloaded and either viewed as a pdf or printed out.
As far as cards go, have a go wayfarer and send me the template (I can open most formats).
Basically something pretty simple.
www.slinging.org fairly prominent and a slinging logo.
I wasn't envisaging a whole lot of actual 'designing'
In fact - let's have us a competition.