This is the 2164th most frequent Korean word.
있거나
"있거나" means "to exist or have, or (used to connect alternatives)."
있거나 is used here to list alternative items that could be inside the bag.
가방 안에 책이 있거나 공책이 있어요.
Either there are books or notebooks in the bag.
있거나's structure, -거나, is used to express alternatives or choices between actions.
식당에 가거나 카페에 가고 싶어요.
I want to either go to a restaurant or go to a café.
있거나 is used here to indicate either one situation or another being true.