while one is at it; incidentally; on the occasion of
Used when doing something extra or additional while already engaged in another activity, or when taking the opportunity to do something. Often translates to 'while I'm at it', 'on my way', or 'by the way'.
If you're going shopping, stop by the post office while you're at it.
Incidentally, tomorrow's meeting has been canceled.
I did some sightseeing while I was on my business trip.
While going shopping, I also returned a book to the library.
While on a business trip, I dropped by my parents' house.
If you're going to the convenience store, could you take out the trash while you're at it?