With that, I've got a few.
Someone near me opened up a package of canned cat food which was covered with moving grains of rice. ... Took a few moments of confusion to realize that wasn't rice since how rice doesn't crawl around.
Someone else had opened up a shoe box in the fitting room to find it covered in feces.
The material was not identified, but one of the backroom guys picked up a coat and just as he was about to put it on, someone told him not to. He looked at it and it was partly coated in a brown sludge. I sincerely hope (and continue to believe) it was just mud from ice and dirt in the freezer.
Me, I opened up a top lid to some pumpkins they keep storing in the hot backroom area for some reason (rather than somewhere cooler0 and all I could see was a carpet of green. Out went 50 pumpkins.
Found a package of mushrooms (when they moved to cardboard plain to black), with no mushrooms that hadn't been rotated properly and it took me a few seconds to realize that there were mushrooms in there... they had simply turned to black sludge (which quite frankly I didn't think was possible).