Your PS2 will come with absolutely everything that you need to play. Just hook it up to the TV and you're ready to go.

As for Memory cards, a single 8MB card should be enough for your PS2 games, but for the PSOne titles (VII-IX plus compilations) you'll need a 1MB PSOne memory card.

So to recap, a PS2 straight out of the box, a PS2 memory card and a PSOne memory card will be all you need.