I'm cheating a bit here as the first two are mine and Ruth's newly published shawl and blanket -- Caribbean shawl and Tesselated Tiles but as Ruth knitted most of the former in the Caribbean sunshine it definitely fits the bill!
Breton tops are always a popular summer look and one of my favourite designers, Isabell Kraemer has one in her Raverly store called 'A HInt of Summer'. It's knitted in laceweight or a light 4-ply so won't be too warm to wear during most of a British summer but brings some gallic charm to our sometimes rain-soaked shores.
As festival season approaches you might want to knit or crochet a festival hair garland. This one is by Monika Sirna and would use up any scraps you have lurking in your stash. The little summer bugs are from Summer Garden by Sarah Gasson and could be used on garlands or finger puppets or make as little brooches for children (or you!)
Finally the Bubblewrap Crescent shawl by Kieran Foley is full of the colours of Summer and would make a useful cover-up as it cools down at the end of the day.
Why don't you take a trawl through www.ravelry.com and find more projects to while away those long summer evenings.