You’re in luck, as I think that’s a reasonable list. The only challenge might be on the size: it’s difficult to disguise 1,800 cubic inches, no matter how “low profile” you make it.
One good pack, designed specifically for skiing, is the DAKINE Heli-Pro ($80; www.dakine.com), featuring 1,100 cubic inches of space to stow spare mittens, some Snickers bars, a small first-aid kit, and a jacket. It’ll hold a hydration bladder, too, plus it has outside straps designed to hold a snow shovel, skis, or a snowboard. Or, try Osprey’s Eclipse 32 ($149; www.ospreypacks.com), which hits your size target= at 1,900 cubic inches, has ski straps and a shovel slot, could be retrofitted with a hydration bladder, and has a slim design that won’t be too cumbersome on lifts or gondolas. Also, this pack boasts one of Osprey’s excellent suspension systems, so could carry quite a load in comfort. And, it’s a panel loader, although I don’t think the floppy lid issue will be much of a concern.
Some purpose-build hydration packs would also work. An example: CamelBak’s SnowDAWG ($75; www.camelbak.com), which has a surprising amount of space at 1,200 cubic inches (although part of that is taken up by the bladder). The Backcountry Access Stash ($145; www.backcountrystore.com) is another very clever option. It holds a hydration bladder, and even has an insulated slot in the shoulder strap for the bite valve and hose, so they won’t freeze up in cold weather. It’s somewhat on the large size at 2,400 cubic inches, but is also really ski-specific, with straps and stow slots for skis, shovels, and other gear. Very nice indeed!