How were portable liquid vessels (like waterskins, gourds, or bottles) sealed when/where cork or metal/plastic caps weren't available?
Stationary pots can be covered in clay or fabric, but I'm more curious about the sort of containers that a person might carry around with them where you need a strong seal. I know bison bladders, waterskins, and gourds were common ways to store liquid in the past, but how would they have been sealed to contain the liquid? Cork is the obvious choice today, but those trees have a fairly limited range, just around the Mediterranean, but bison bladders were common among plains peoples in North America so they must've been using something else.
Are there more widespread trees which might be chosen? Are there other materials that would make a good stopper besides wood?