How much does your 30L pack weigh? I carry a Deuter Speedlite 30L inside my main pack while I climb the mountain and then use it on summit day. The pack only weighs 650 grams but there are several others that are lighter.

The Deuter 30 is the pack I've carried each time on the three day trek to Plaza Argentina. In it I only carry a water bladder, headlamp, suncreen, lip balm, toilet paper, camera, small lunch, water treatment drops, all my identification and money, sandals (for the river crossing on Day 3) and my Primaloft jacket (in case the mules don't arrive at camp before the sun goes down). Everything else goes in my duffel bags that should be at each camp you stop at along the way. If you want I could send you a copy of my gear lists for the trek in, camps 1 and 2 and summit day. Just send me an email.

I saw a 12-year girl on summit with a "Hello Kittie" backpack. As long as you are willing to carry it, it's fine. My partner and I used our giant backpack all the way, then left the pack at the base of Cantaleta and just use the lid of our backpacks.

What divnamite said. Use whatever you want if you're willing to carry it with you. There are no rules here and you'll see climbers with all different combinations of gear on the mountain. The only thing I try to do is have fun and enjoy it.

A 20 or 30 liter light pack should be fine for either the Normal or False Polish Traverse routes depending on your level of comfort and safety with respect to the amount of gear you wish to carry.