I've tried several lightweight, medium-capacity (~30L) packs for 'day' use. For me that means a 5-10 mile weekend hike with the dog and bringing along lunch, water, dog snacks, rain gear, GPS, trekking poles, camera, and sometimes, my heavy Manfrotto tripod. So far the best I've found is the Deuter Futura 32BC (
http://www.rei.com/product/797596) for about $130.
Here's why:
First and foremost is the suspension system. The Deuter simply fits better than any other pack I've yet tried, including several larger ones at 3 or 4 times the price. That doesn't mean it'll necessarily fit you as well as it does me, but it seems like a pretty good reason to start with that model. The spring-steel side stays support a taut mesh back panel that provides outstanding ventilation on even the hottest days.
Second, the pack has an optional zip-up divider in the main pocket which, together with the lower zip-up outside access panel, means you can effectively convert the main bag into a 2/1 configuration to keep lighter gear like clothing at the bottom where it'll provide cushioning for you camera gear in the upper two-thirds. At 32 liters (~2,000 cubic inches), it's large enough for a 2-season ultralight overnighter.
Third, the pack has a waterproof stowaway rain cover that fits neatly in a bottom pocket, ready to break out and cover the pack to protect the contents from a downpour.
Finally, it's got a better-than-average array of external zip pockets, compression straps, mesh water bottle pockets and lash points along with an internal hydration sleeve to fit your Camelback or other water bladder.
In fairness, at 3 lbs 10 oz it's actually heavier than the 60 liter REI Flash 60 I just bought for weekend trips. But the REI pack lacks many of the creature comforts of the Deuter making it seem Spartan by comparison.
Give one a look at your nearest REI store.
K