List of sour things:
Lemons
Oranges
Grapes (sometimes)
Green apples
Vinegar
Mango (unripe)
Yogurt (sometimes)
Gastric acid
Batteries
Sumac
كركديه
حمّيض
Coffee (from freshly roasted beans)
Kiwi
Kimchi
Ants
Labna (labneh)
Candy (some types)