Aunt & Niece Keepsake?

I am a new aunt who is very excited and wants to be very involved in her life. What can I do for keepsake/memories? I was thinking of writing her a letter every year of her life and gifting it to her on her 16th birthday? But I really need some ideas! It can be a gift for her as a newborn, or something I have to wait to gift her till she’s old enough! I need all the help!