Optional items for a day hike, like a headlamp and warm ski hat, become essential when you’re spending the night outside. The same goes with rain pants—even in dry weather, you might want to throw them on at the campsite for warmth and protection from biting bugs. And while you’ll bring the day-hike outfit of a synthetic shirt, fleece layer, and breathable rain jacket, on an overnight, it can’t hurt to pack an extra warm layer, like a light down vest, in case you get severely chilled. Bring one pair of wool socks, made by a company like SmartWool, per day. Instead of bringing just one water bottle, it’s good to take two.