Expressions (phrases, clauses, etc.)
taking the opportunity to do something; doing something incidentally; doing something while (you) are at it; doing something on the way; while I'm at it
Idiomatic expression
Also written 行きがけの駄賃【いきがけのだちん】、いきがけの駄賃【いきがけのだちん】、ゆきがけの駄賃【ゆきがけのだちん】