The sun’s shining, the days go on for ever and ever, you’re dying to be out in a field getting your ear-drums blasted out by industrial speakers while ingesting some mixture of cider, organic sausages and mud. It’s festival season. You’ve packed the tin-opener. What else do you need? Here are some gadgets to make that stay under polythene in a field much more fun – for you, and everyone sharing the tent with you..