Holiday list? what to bring!?

hey guys quick question! im going on holidays with my anty and her kids and husbacd, im so stuck at to what to bring though! im a really big packer! i bring loads and loads and loads of stuff and ony end up wearing a quater of it if even that! im going to be in portugal so i dont know if its going to be sunny or cold? or what we will be doing, i know were going to parrot shows and that craic cause the boys are only young,! my mam told me that im only allowed 20kg, i dont even know if thats big or not? can someone give me a reasonable answer, teenagers if possible because im only 16! thanks for readingg:)