Go for fruits with high water content like water melons,grape fruits,oranges,pears and peaches.Ripe mangoes are not really cool but raw mangoes are! During summer juice of raw mango is extracted and consumed as "aam panna".It cools your body. Coconut kernel and water can help .One fruit that helps cooling is the bael fruit. I don't think you can have it as the whole fruit but extract the yellow pulp of the ripe fruit, mix it with lime juice and have it. But it's not very common. Also you can have cool things like the cucumber or juicy tomatoes.Apricots and strawberries are also juicy and yummy.