I love this thread!
I used to have a Gameboy fanny pack that I bought just to make a silly video (it was going to house a TurboExpress), but the footage was crappy and I gave the fanny pack to a huge Gameboy lover.
Anyway..
I have been using old baby formula bags (my daughter is now 13, ha!) for my solo PCE consoles. AC adapter + controller + cables all fit in the the console (different pockets).
Since it was padded ("insulated") for baby formula, there is some decent protection from bumps and bruises. And an over-the-shoulder shoulder strap, for maximum mobility.
I USED THIS out of desperation, of course.
I moved across country in 2006 and I didn't know how I was going to safely transport all of my consoles/handhelds...so I just used random stuff I was going to otherwise donate/throw out.
SMS wrapped in several diaper mats, then shoved in a diaper bag. I think it shared the bag with FC, cushioned with small baby formula cooler bags.
3DO and DUO and stuff were in laptop bags (my wife got a ridiculous number for free because nobody at her work liked the huge, bulky DELL bags issued with their laptops).
I am very happy with all these stoopid padded bags, since I only keep 1-2 consoles out at a time.