Use 'into the bargain' to indicate something extra that's positive or advantageous. He bought a car and got a free GPS into the bargain.
Pro Tip 2/3
Surprise Element
It often implies a surprise or something unexpected in addition to the main thing. The hotel was comfortable and we got an amazing view into the bargain!
Pro Tip 3/3
Not Always Literal
'Into the bargain' is sometimes used in a non-literal sense, focusing on added value rather than a deal. He's a great player and a good sportsman into the bargain.