If you’re planning on picking up Dead Island Definitive Edition at retail, depending on which version you get there are different things in the box. One version has all three games on the disc. One only includes one and codes.
On Xbox One, your disc will include Dead Island, Dead Island Riptide, and the bonus Dead Island Retro Revenge brawler. On PlayStation 4, the disc is a little thinner (metaphorically).
That platform only includes Dead Island Definitive Edition on the disc. The other two items are acquired via download using included redemption codes.
If you happen to live in an internet-poor area, this is something to keep in mind.