Caspian: He never gives you the same birthday gift. He makes really effort to give something new and really good. Maybe something that involves culture, or art, or something like that... Once, he took you to a theater.
Peter: He always lose himself thinking about what to buy for you, because you want so many things... So, he always end up giving you money so you can buy your birthday gift by yourself. And you actually love when he does this!
Edmund: He is used to buy your birthday gift with antecedence. So you always discover what it is even before your birthday come. Most of the times, he gives you a book, with a bouquet of flowers.
Eustace: He tries to surprise you every single birthday. So he always gives you random gifts, from the most cute thing to a totally huge crazy one. The last one was two tickets for a tour of some of your favorite bands.