20 oz tumbler where you can see like a rotated version of the complete tumbler wrap
Using any background/scenario that are currently in place and available on your mockups is just fine, it's more about the subject matter, having what appears to be 3 tumblers side by side, showing the different side/sections of the full wrap.
No models needed, prefer the tumblers sitting side by side on flat surface/desktop/counter/etc.
have included a sample image from a random item on etsy, (titled "sample" of the pittsburg steelers) so that you can see the "flatness" of their mockup, (the resolution isn't the best as I took a snip-it of their image but it's much better on their direct image on the website), and I also included one I tried to "piece" together using the method I described above, (titled "mockup all") where I C&P snip-its all together, which shows the image degradation of this process.
not sure what all the different sellers that use this type of advertising use but it definitely looks like a placeit style mockup of the design on the tumbler, as the images of the wraps on the tumblers are very flat and non-dimensional.