I think the overall standard that Charles set from the outset was that items needed to have a casino name/logo on them. That is, a cocktail napkin that says "Sands Las Vegas" would qualify, but a plain white napkin would not ... even it the napkin-harvester provided a notarized affidavit that he or she personally procured it at the main lounge at the Sands after a brutal beating at the tables!

Besides, the sugar cube you reference was for a Caribbean casino, and we all know Charles is an advanced collector for all things from "the Islands".

(pic courtesy of the Chip Guide)