My girlfriend's 18th Birthday. Gift?

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I just wanna surprise my girlfriend on her upcoming 18th birthday on July and I want your advice regarding what I will give to her as my gift. Where're already been gf/bf since 2008. But the sad part on it is I will not attend on her debut party because we are not legal partner on her part. Because her parents is so strict. Can you give me some advice? Though, I will attend, I wanna surprise her.