Basics:
Form-fitting tshirts (especially graphic tees), you can find them almost anywhere, neon colours, 2000s style designs
Low rise jeans, bootcut and skinny, ripped jeans, any colours, jean shorts
Anything leopard/zebra print (especially bright colours!!)
Pleated skirts (Tartan, patterned), tutus
Long stripy socks and tights
Accessories:
Kandi jewellery, rubber bracelets, loom bands
Hairbows, cute hair clips
Studded bracelets and belts!
Also don't forget hairstyles!! Almost any 2000s style outfit can be scene if you have the right hair! Big volume, side part, bangs (if you can have them)
And don't think that you have to buy the most popular stapes, or shein clothes, a thrift store will have 80% of the things you're looking for!!