To play most types of poker, you are going to need:

1 Deck of Cards, brand doesn't matter, though I prefer Bicycles. Note: You may need more than one deck if you are playing with a lot of people.

At least 3 friends, if you are playing for money; if not, it is possible to play by yourself, but not very fun. 1 friend should do, but the more, the merrier.

Optional: Card table, but regular tables work, and you need somewhere to put your cards.

Optional: Money, if you are betting.