Simond MT500 Compact Zip-Together Synthetic Sleeping Bag 10°C

Festival nights get colder than the daytime heat suggests, and this bag is sized for exactly that: comfortable to 10°C (50°F), with a limit of 5°C (41°F) and a hood you can cinch up when the dew comes down. Synthetic fill and a water-shedding outer fabric suit a tent full of damp clothes, and you will not fret over it the way you would a pricey down bag. It packs to 8 L in its compression sack and weighs about 900 g in size L, so it slips into a backpack alongside everything else. Two of these zip together, which suits couples sharing a tent, and the price is low enough that a muddy weekend will not hurt.