Well, not many of those types of stores around Downtown Detroit by Cobo. Those are more of community stores (Kmart and Pep Boys) and they aren't near the riverfront. If you haven't yet, check out
www.naias.com which has some info. I think they send you to
www.visitdetroit.com for hotel info. The tunnel puts you about half a mile from cobo on the same road. Gas, I don't know of any stations right on Jefferson, the road the tunnel puts you on and Cobo hall is on/over.
Any more specific q's?