Tommee Tippee Magic Mat
As far as I can tell, this is the same as the Tommee Tippee Magic Mat I got when son first started weaning. Basically it is a sort of plastic mat that also has a non-slip surface. I got it so that he could feed himself when we were out, without also dragging the plate or bowl off the table.
Unfortunately it doesn't stop them from picking up the plate and throwing it on the floor if that's what your toddler really, really wants to do! It is a magic mat - just not THAT magic. But the sucker does work, and if you're at a restaurant it saves you a lot of mess.
I also had one of those little material portable high chairs, the kind you can use with most sorts of dining chairs. The combination helped him be able to join in at the dinner table where ever we went, even if there wasn't a high chair.
The mat itself worked really well with all the plates we used. So no accidental knocks at all, just the on-purpose, I'm determined to do this, kind. The non-slip surface also helped steady cups when he was trying to be all independent, picking up and putting down himself.
Another major plus is how easy to clean it is, and also how it keeps looking just like new. Even now, 7 years later. Yes, I am still using it. Although now the mat sits on a shelf in my kitchen. There's a few items that I like, and I want to keep, like a gorgeous fruit bowl. It is hard to keep nice things when you've boys in particular. The non-slip mat stops me from knocking them over by accident, or anyone else. Also, again, it is easy to whip off and keep clean. And the blue colour matches my kitchen decor!