Sadly, at most venues where one might have a mug, in the US it generally is illegal to transport a drink from one bar/tavern to the next. (I was once informed in a Pennsylvania bar that it was illegal to have a glass in hand while standing up, and was severely chastised for taking my own drink from the bar to join friends at a table.)

At most festivals in my immediate locale, "spirits" of all sorts are strictly prohibited and not for sale. That usually means bringing your own, and pouring it discretely into an unlabelled container so that you can pretend it's "sody pop" or "lemonade." For this, a tankard might be of use.

Pewter was, according to what I've heard, a sort of "class thing" since metal vessels of any kind were too expensive for the peasants, so a pewter mug would be a status thing. As to folkish authenticity, it would then depend on what "social stratum" you wished to represent.(?)

It should be noted that some pewter had high lead content and could cause "drain bamage" if used regularly. That would hardly be noticed for some dancing troupes, but might be of concern to musicians. In the US, lead-pewter wasn't reliably removed from commercial channels until perhaps the 1940s, so mugs older than that might be suspect.

Modern (non-lead bearing) pewter is safe enough, but it's always been my impression that any kind of metal container affects the flavor. I've had a number of "pewter" mugs (although a couple were clearly alumin(i)um in drag) and have not found one that I enjoyed using because of the "edge" on the flavor. (Note: commercial beer/beverage cans, at least here, are copiously lined with "lacquer" so that there is no metal contact with the contents.) The flavor effect might be less noticed with stronger flavored beverages of the kind more popular in differently-civilized parts of the world.

When I need a "carry mug" in camp, I generally just use a quart "mason jar" with a screw on lid (sort of a tradition in my part of the US), so that I can cap it to keep the bugs out and the lid is secure enough that if it's necessary to kick it out of sight nothing spills. I have rigged a "necklace" to carry one, but don't usually bother with it.

I may be a bit fussy, but I've NEVER seen a plastic container of any kind that was really fit to drink out of, although sometimes there just isn't a way to avoid it (esp. if being polite is an issue).

John