i've only been to ibiza once, but going for my second trip in 3weeks, when i was there anything goes, fashion, bright colours, bikinis, whatever.
i wear what am comfy in and cool, i bought loads new clothes, loads floaty BRIGHT tops keep cool, i'm just wearing normal going out clothes you'd wear here but brighter! i'm taking wedges, can last longer in them and glittery flip flops for when my feet really hurt! and wee bags that wear over me so i can dance the night away.
hope that helps.. but basically wear what u want.