I have a mug like the red one on Aslowhand’s post, it came in a Swedish Army surplus M-40 stainless steel mess kit. I believe the cups are called kuksa kasa, ideally shaped of durable plastic, to warm cold hands, being pear shaped and well rounded to fit between cupped hands. Modern ones are made by Wildo in Sweden in many colors not just Army green.
Also have a couple of really old what I thought were called Cascade Cups, sturdy stainless steel manufactured just like a Sierra Cup but with a straighter side so that the bottom is nearly the same size as the top. I think it is the same as Conk’s Rocky Cup and quite possibly is a a Rocky Cup. Like all really good stuff is no longer made. I haven’t seen them since I was last in Minnesota. They reside inside a GSI stainless Glacier pot in a box with other camp kit equipment, behind my friend Jeff’s couch awaiting my next Boundary Waters trip.
My current favorite cups are my daily at home, on the road or in camp MiiR double walled stainless steel, green or blue with white speckled enameled painted insulated cups. They come with a sipping lid to keep kamikaze mosquitoes from adding protein to the brew. Other favorite cups are the Finnish Kupilka cup or hand carved from birch burl Kuksa.
Almost forgot to mention another current gem, that was a gift, a ten ounce Hydro Flask stainless steel insulated wine tumbler, is great for sipping hot black tea. Easy to pack along on a day trip, as it takes up hardly any space, fits over the top of my small thermos both ride comfortably in a Duluth Pack Fanny belt pack with sandwich & snacks.