When you're hiking in the heat you'll be wanting a well ventilated pack, and Osprey have created the perfect answer, the Men's Stratos range. The 26 litre capacity version is great for day hikes, giving you space for food, drink and wet or cold weather gear without too much extra space to tempt you into carrying unnecessary extras.
That said, if you're carrying a lot of fluids your pack can still be pretty hefty which is why Osprey have developed the AirSpeed™ ventilated back system based on their renowned AntiGravity™ technology, to make the pack feel as light and comfortable as possible. You're heading out for pleasure not pain after all!
Top opening, with a zipped pocket in the lid and a vertically zipped expanding pocket on the front to stash your microlight down or Gore-Tex jacket. Add to that the ever useful pair of zipped hip-belt pockets plus external hydration access for your water supply and you've a place for everything.