This is a kind and polite parting greeting, meaning "Please return safely." "お気をつけて" (oki wo tsukete) means "Please be careful." It's often said to guests, colleagues, or friends who are leaving, expressing concern for their safe journey home, especially if the weather is bad or it's late.

帰る人に対して、道中気をつけて帰ってくださいと丁寧に気遣う言葉です。