Looking through your list of equipment, I'd guess you have most everything you need or want. What about a little point-n-shoot?
I got an ELPH 330 about a year ago, and it is very interesting to go from a 5DIII to a little Elph. How do you get the picture? How do you make it work? Whereas I have to do a bit of planning to bring the 5DIII, I have to do a bit of thinking to get the shot with the Elph.
There's a YouTube channel for DigitalRev TV for their series Pro Photographer, Cheap Camera. That inspired me, watching some excellent photographers create amazing photos with truly low end cameras. How far can you push a relatively simple digital camera?
I love my little Elph. It's fun and takes great photos under Sunny 16 conditions. It's even more fun trying to get photos when conditions are far less than Sunny 16. It will never replace my 5DIII, but then I never intended that.