Hi @outlander
A couple of weeks ago my MH worker gave me a piece of A4 paper with some cards on it to cut out and keep with me for when I am having a tough moment. I've been meaning to share it with you for a while, just haven't found the right time. Now seems good.
So the idea is called the 'flashback halting protocol' by Babette Rothschild (who I think is sort of great so if you see any of her work or writing I recommend reading it).
It's pretty much the same idea as a lot of the other grounding techniques you know already, though what I love about this one is that the way it was given to me on cards, means I can take one with me almost anywhere.
I found it on pinterest and here is the same as what I have.

It's just a little bigger than a business card.
Keeping one in your purse, stuck somewhere in your car, in the shower (you could get creative and find a way to make it kind of waterproof enough to stick somewhere you might be able to see), under you pillow, as a photo on your phone etc could be useful. There are lots of places this one might come in handy.
There are a few videos and a bit more info about it out there if you're interested and want to google as well.
Just another one to add to the list to try if you'd like (and haven't already) 🙂