I should think that anything around 2,500 cubic inches will suffice. The wild card is whether you need to carry water, and how much. Otherwise, the load you describe will fit nicely into a typical day pack, with room for food and clothing and Wild Turkey.
A great example would be the Osprey Kestrel 38 ($139). It has 2,300 cubic inches of capacity, plus adequate external stowage for poles, a jacket, that sort of thing. It's a simple top-loader with a fixed flap/pocket, so you can't over-fill it much. But you should be fine. And its suspension will take pretty substantial loads, as it has an internal steel frame that gives it structure and transfers weight to the hip belt.
Gregory's Z40 ($149) is cut from very similar cloth. It's just a little bit bigger (2,440 cubic inches), with a rear "shove-it" pocket that gives you a place to externally store some clothing. And it's designed a bit more as a small overnight pack, so has slightly easier access to things such as a sleeping bag. I have a somewhat larger Z-type pack that I use for trips of two and three nights, and it carries extremely well.
Lastly, REI's Flash 50 ($149) gives you 3,000 cubic inches of space in a pack that still is very light yet has an excellent suspension. That's still a pretty compact pack, and you might find the extra space handy seeing as you really are not paying any weight penalty (it's 2 pounds 10 ounce, while the Gregory is 3 pounds three ounces). Not built quite as ruggedly as the Gregory or Osprey, but still plenty durable.
Subscribe to Outside
Save 72% and Get the Special Women's Issue!