Green’s Dictionary of Slang

shuper n.

also shupper
[ety. unknown; ? link to SE super]

(US) a large beer glass.

[US]J. London Road 120: My pal and I were in a saloon. Two foaming shupers were before us.
[US] ‘Jargon of the Und.’ in DN V 462: Shupper, A schooner of beer.