I don't do tubeless so I have no idea if this would work there, but - with tubed tires you can often repair large cuts with a boot of material as strong and stretch-proof as the tire itself. I have repaired many tires, sometimes with slices clear through the casing as long as 3/4" with sailcloth. (NOT the "sailcloth" at a fabric store but the real Dacron sailcloth used to make sailboat sails.) Glued in with contractor grade contact cement (the stuff countertops are glued down with), the patch is part of the tire and will outlast the rest of the tire. Make the patch much bigger than the cut.

On the road, dollar bills are impressive for the wide variety of cuts they can deal with and get you home. I make it a point of riding with at least 5 of them (any denomination - they survive just fine but might have to go through the wash before further use). For cuts close to the bead, I've started the bills under the bead so they are anchored securely when you inflate the tire.

I bet if you went to a sailmaker and asked nicely, he'd give you a scrap of cloth appropriate for an old-school racing dinghy that would keep you in boots for many years.