Your partner ascribes to the One-Kitchen-Pot view of pack size, based on the notion that one big pot can handle everything from heating a can of soup to making pasta for 12. If all you want or can afford is the one pot, then best to get one that can handle everything. So, your friend is partly right. Get one big pack, and if you only half fill it for a climbing day trip, no big deal. The risk is that you buy a pack that’s so big you end up packing stuff you could likely live without, resulting in a heavy, heavy load on multi-day trips.
But giving advice on the “ideal” pack size is tricky. I typically don’t mind packing a few extra creature comforts, so for me a 5,500-cubic-inch pack is about right for trips of more than a few days. Some people think I’m remarkably frugal, others that I carry enough to supply the Third Armored Division for a week. Yes, I admit it, I could pack more efficiently.
Of course, it’s also true that smaller people don’t necessarily get to carry smaller loads. Sleeping bags, tents, stoves, food, fuel聴all that stuff is pretty similar for people of all sizes. For you, though, I’d say you could get by with a pack that carries 4,500 cubic inches or less. That’ll ensure you can take what you need, but aren’t carrying too much. Packs in this range include the Gregory Forrester ($240; www.gregorypacks.com), Mountainsmith Chimera ($260; www.mountainsmith.com), Osprey Aether 75 ($240; www.ospreypacks.com), and Dana Design Glacier ($299; www.danadesign.com). All are good load-haulers, the Glacier probably being the biggest and best with heavy, dense loads. (It’s also on sale from Northern Mountain Supply for $180.) But for the 40-pound loads you probably have in mind, all of the above are very capable. What it boils down to is the best fit, so try on several for size before you buy.