X Party Belt
X Party Contact Lenses
X Birthday Dress
XX Party Shoes
Party Flower
X Party Jacket
x Slice of Birthday Cake
X Party Runners
XX Party Pants
X Party Skirt
XX Party Trousers
XX Party Top
Party Wig
XX Party Hat Plushie
III Party Tiara
III 10th Birthday Hat

There is 1 Hidden Avatar associated with this treasure chest, the Party Chest Avatar.
[Image link blocked] Party Chest Avatar - Open a Party Treasure Chest.