The guy who sits next to the window just confettied some mean girl on her last day. He built a whole contraption and everything. I thought he was building a cardboard thermostat for the air conditioning vent. He wasn't, but it was still pretty great. It also has nothing to do with backpacks. I guess this is supposed to be about backpacks. First up there are day hike packs. A daypack is just the right size for, yeah, a day hike, to fit your gear and a jacket, some snacks... that kind of stuff. Larger day packs can be used for fast and light overnight trips. Like super light.
If you're taking more gear and staying overnight with a tent bigger than a tarp shelter you'll want a larger, multi-day pack. These packs are good for fast and light weekends or three day backpacking trips, or an overnight camp. A weekend size backpack will hold a lightweight tent, sleeping bag, sleeping pad, cookware and food.
For extended trekking expeditions and smuggling melons across the Ohio border, check out expedition size packs for all your gear. Expedition packs are like real serious backpacking backpacks. That's weird to say: backpacking backpackers' backpacks. Anyway, check out trekking packs from sweet brands like Osprey and Lowe Alpine.
Technical backpacks, or activity-specific, packs can totally come in handy when you need just exactly the right pack for whatever silly thing you're doing. Check out climbing backpacks for rock climbing, bouldering from Arc'teryx and Black Diamond. If you're adventure racing or going on a longer trail run, you might check out a running backpack or a lumbar pack. Check out ski and snowboard backpacks for backcountry powder extravaganzas.
If you're not into actually doing stuff, and you'd rather just hang out and look cool, check out some of the more casual packs. They're the kind of every day backpacks, like work backpacks and school backpacks, from Patagonia or The North Face are really where it's at right now for people who like to carry stuff on their backs. Check out laptop backpacks that have a special protective sleeve for your computer.
I was at the train station in Klagenfurt and everyone had these really cool travel packs, and I knew they were serious about this whole travel thing. Some of the Osprey travel backpacks have a detachable daypack, so you can leave your gear back at wherever you're staying. It's like two packs in one. That like almost never happens.