shrewdly; smartly; opportunistically — describes someone who is sly or quick to take advantage of situations for their benefit.
彼女はちゃっかり割引券を使って安く買っていた。
She cleverly used a coupon and bought it cheaply.
あの人はちゃっかりしていて、先に席を取った。
That person was sly and grabbed a seat first.
本人は大変そうに見えたけど、ちゃっかりメリットを受け取っていた。
He looked like he was struggling, but he was smartly getting the benefits.