Try Deuter's women-specific Aircontact 60+10SL ($249; deuterusa.com). The 112-year-old company was one of the first to make both a women's-specific pack and a ventilated back system. Combine the two and you've got a very comfortable pack--at least that's how it felt when I took it on a backcountry snowshoe excursion to New Mexico's Lake Peak a few weeks ago.
The secret to this five lb., 13 oz. pack's comfort is a system Deuter calls Aircontact. It's a foam that creates a "pump" effect through compression and expansion as you move, which effectively makes you and the pack move as one, which in turn makes it easier to carry a big load.
Additionally, the Aircomfort has an easy-to-adjust fit, a hip belt that saves wear and tear on your lower back, a bottom compartment with zipper access to the main compartment, a carrying capacity of 60 pounds, a detachable rain cover, side bellows pockets for cramming the emergency puffy jacket, big side water pockets, a detachable rain cover, a pole and ice-ax attachments, and it's also compatible with a hydration system. If you need more space, strap on an additional set of two 8 oz. External Pockets ($20 per pair).
If you're looking for the ultimate daypack, try Mountain Hardwear's Trad ($130; mountainhardwear.com). The three lb., two oz., 35L pack, new this spring, seems bottomless. Designed for trekking, hiking, climbing, skiing, or any other hard-core use you can think of, it's got heavy-duty 630D ripstop nylon on the front, bottom, and side panels and all the gear-specific necessities you need, like heavy-webbing ski loops and a daisy chain running down the front. The padded air mesh back panel keeps you cool and there are so many pockets (always a bonus) that I sometimes forget where I stashed my iPhone. Best of all, its "On-The-Fly" compression system allows you to adjust your load on the move.As for what to put in your pack, the list can be as endless as the amount of space you have. But my short list would include a First-Aid Kit, a headlamp, a multi-tool, and something good to read.