"케이크를 사 오세요" Neither "buy and bring" nor "buy and come" sounds natural, but the former is better. For example, "buy and bring a cake" works, whereas "buy and come a cake" doesn't. When two languages are drastically different, such a literal translation makes little sense. If no one will ever say it like that what's the point of it? It would be more useful to translate assuming some probable contexts. For example, a wife might ask her husband to buy a cake on his way home. - (오는 길에) 케이크를 사 오세요 = Buy a cake on your way home. Or she might ask her husband who's home: - (나가서) 케이크를 사 오세요 = Please go get a cake (for dinner, or whatever). Or a cooking teacher might ask her students to bring a homemade cake. - (집에서) 케이크를 만들어 오세요 = Bring a cake you made yourself at home. As you see, the expressions vary a lot depending on the context. It might make learning more difficult but such realistic expressions are the real meaningful ones.