while you're at it; take the opportunity to
Used when doing something as a natural extension of another action, often with a sense of convenience. Frequently appears in the pattern 〜のついでに or 〜ついでに. The expression 物のついで is a set phrase meaning 'since you're already doing one thing, you might as well do another.'
See also: ことのついで
If you're going shopping, stop by the post office while you're at it.
Since I started cleaning, I'll wipe the windows while I'm at it.
Standard kanji-kana mixed spelling. The expression is usually written in kana.
Alternate kanji form using 序で; less common than 物のついで.
From 物 (thing) + の (possessive particle) + ついで (opportunity, occasion). The word ついで originally meant 'order' or 'sequence', and by extension came to mean 'an opportunity arising from a sequence of events'.