Niall:
You both love to play guitar, and since you always complain about your guitar being both old and bad he gives you a new one. Exactly the one you had wished for. He also put a little extra detail on the guitar - your name.
Harry:
He knows how much you love the Harry Potter-books so he gets you a special complete collection of all seven books. And a necklace with an H on it - matching the one he gets himself with the first letter in your name.
Louis:
He gives you a special bracelet. It's silver with a little gold design on it. On the inside it has written a little sentence that he picked himself: "Trust me. Hold me. Love me."
Liam:
He takes you to dinner at a romantic restaurant as his present. He's made sure that no fans will be interrupting you, and that it's just you and him for the evening. He's also gotten you a necklace with a heart.
Zayn:
He knows that you don't like it when he spends a lot of money on you, so he doesn't give you anything big. A simple box of chocolate. The chocolates are not that simple though - on every piece of chocolate there is a letter or a little heart. It spells out "I love you Y/N".