How to avoid having to go to a party?

Kso, i've been invited to a party tomorrow but i got the news late thus i don't have a present nor a card to give her and i don't really want to go get one (im lazy). I don't want to show up empty-handed either, but the dilemma is that she really wants me to come. Do you have any ideas on how to avoid going to the party WITHOUT being mean and WITHOUT saying that I already have plans because she knows im free tomorrow. Much thanks.