Rubber is a toughie though. (that sure doesn't look like it's made out of leather.)
Harvesting and using rubber tree sap would be well within what medieval technology could do - the main issue is that rubber trees aren't native to Europe, and most of these fantasy settings are in a Europe-like environment. Accordingly, plants and animals are typically either native to Europe or come from the D&D Monster Manual.
Rathurue said:
Easy, just use some slime skin! (they're in medieval fantasy, after all).
This one I'll buy - a slime seems more likely than rubber trees to be a thing you'd encounter in this setting.
A lost child!
Will she really be alright though...
Papaa...
Got any leads, Syrup?
Oh!
Papa...
Syrup went out by herself to recruit some companions.