Shorts, T-shirts, swimmies (Alberdini has a pool), a pair of long trousers and something with long sleeves in case it gets cool in the evening (not likely given previous years).
Loads of cash, several credit cards, drinking boots, ibrupofen (for trail injuries), paracetemol (for bar injuries), E111 card, spare cash, passport, driving licence, V5, insurance, more cash.