The supplied case is fine if you want to fold everything up as per shipping, but I want to set up the camera balance etc hence moving the arms to the point where it won't fit back in its case.  So want to just take off the battery and drop the 2 pieces in a case.

Any recommendations of small backpacks or cases that work well?

When (if) I get mine, I plan on setting up a Pelican to deal with this.

You should look for a bag with a decent pocket in the front.
Something like Tenba Solstice.
I just came home from a short trip where i had the Ronin S stretched out without the grip in the front pocket. The rest was filled with clothes. This was just a regular smalish backpack.
I am thinking about buying either the 20L or 24L of the linked packs, but i am unable to try it before purchasing. And i am still waiting for my new camera. 5DMkIV

I too am looking/thinking of a carry solution. As for locking the gimbal for carrying, I ditched the velcro strap for a custom made bungee cord. Similar to the Think Tank red whips, only the Think Tank whips are too short so I made my own. I have found the the bungee cord is easier than the velcro strap.

I just throw it into my Lowepro 450, it's pretty durable

Using a bag from Peak Design works great.
See this Article: https://konkludenz.de/reisetasche-fuer-den-dji-ronin-s/
Sorry it is written in german. Please see this Google Translate link (english): https://bit.ly/2Nrhp5t

anyone try the ronin-s w/ an sony a6300  with think tank retrospective 5 or 7 v2

I saw this bag from Portabrace--seems interesting. https://www.portabrace.com/car-ronins.html but a bit pricey.
I think a carrying sling is probably in my future as I'm not sure how I will lug it around the city.  I see some carrying slings that attach to a mount with mounting points for other accessories, so that might be the best option.

EAPS Posted at 2018-8-7 10:30
I just throw it into my Lowepro 450, it's pretty durable

My Ronin-S will arrive next week, and I'm thinking of using the same bag (Lowepro 450AW) for a trip. Do you still think it's good to hold it in place and safe?

I use my Manfrotto Advanced Travel Backpack to carry 5dIII + 3 lenses + Ronin S. Battery grip with legs fits into the side tripod department.