For what in particular? Water jacket doors? Plumbing connections?
"Beer box" thickness has worked everywhere I've used it
I keep a range of various "oil safe" gasket card but couldn't tell you off the top of my head. 0.4mm and 0.75mm maybe , and yes quite a few times a literal beer box.
One of my bug-bears is poorly fitting gasket surfaces. I bought a recipro pump a few years back "reconditioned" (reconditioned by Dulux, as we say here - just painted! Asswipes.)
Any way, the valve cover came with a 1/4" rubber gasket, cranked down hard, which should have rung alarm bells,
I chucked up the cover in the lathe and skimmed it flat, and took to the mating face on the housing with a file, sealed up beaut with beer-box after that.
You don't really need to overthink it, gaskets -usually- aren't used to set tolerances. (Under lister CS head is an exception)