Thats a straightforward question, but of course there are a few variables to the answer. It depends on the type of trip youre planningguided, or un-guidedand what time of year.
Lets say youre doing the normal routine: Paradise Lodge to Camp Muir, a night at Muir, then on to the summit the next day, and then back out to Paradise. That is a trip you will not forget, at least not until the pain in your thighs subsides, and that could take weeks. I cannot emphasize enough the sheer brutality of such a trip. Its not getting up the thingsomething most reasonably fit people can manageits coming all the way down the same day.
But I digress. For that trip youre carrying clothing, sleeping bag, probably half a tent (assuming you're with someone), cooking kit, etc. Youll need at least 4,500 cubic inches in most cases, and maybe 5,000. That would be a pack such as Gregorys Lassen (4,525 cubic inches, $319; www.gregorypacks.com), Osprey Crescent 85 (5,100 cubic inches, $379; www.osperypacks.com), or Kelty Tornado 4900 (4,900 cubic inches, $180; www.kelty.com). You dont need a summit pack"just carry the mostly empty big pack top the top. And all of these packs have good suspensions (pay more, get a better one), plenty of tie-on points for ropes and crampons, and good volume.
On the other hand, lets say youre climbing in July or August (this could apply for Scenario One as well). The weather forecast is benign (caveat: never assume good weather on Rainier), and youre either on a guided trip and will be sleeping in a hut or using the public climbing hut at Camp Muir (recently remodeled and, for now, mouse-free). Lets say as well that youre packing modern, lightweight rain shell and pants (Patagonia Stash jacket, $225, and Rain Shadow Pants, $80; www.patagonia.com), maybe a soft shell jacket (ArcTeryx Gamma SV, $259; www.arcteryx.com), light down-filled 30-degree sleeping bag (Marmot Arroyo, $249; www.marmot.com), etc. Then you might not have more than 4,000 cubic inches worth of stuff, and you could haul a lightweight pack such as REIs Cruise UL 60 ($130; www.rei.com), which has just under 4,000 cubic inches of capacity in a package that weighs only three pounds, two ounces.
Hope you have a great trip! Luckily for you, theres lots of good, steep day hikes in your area for training. Oh, wait, you live in Michigan! So I guess its a Stairmaster for you, pal.
Youve got your winter gear, now get outside and use it. Away.coms ski and snowboard guide makes it easy to find nearby slopes just begging for fresh tracks.