A polite expression requesting someone to take care of their health/well-being; often used in letters or messages (meaning 'please take care of yourself').
忙しい毎日ですが、どうぞご自愛ください。
I know you're busy every day, but please take care of yourself.
体調を崩しやすい時期ですので、ご自愛ください。
It's a season when people easily get sick, so please take care of yourself.
ご自愛ください、またお会いできる日を楽しみにしています。
Please take care of yourself — I look forward to the day we can meet again.