Just for fun I thought I would try packing my gear into the book bag I used to use in college. It was a giant LL Bean Super Deluxe book bag. When full, it sticks out about a foot from your back. I got teased a lot, but since I commuted to school on a scooter from my house in the mountains, I had to carry around rain gear and jackets and needed all that space to store them, in addition to my books. It holds something like 2200 cubic inches.
My gear fits in there with room to spare for food. Theoretically, I could go backpacking with just my book bag. I would try it except that the zipper is broken, thanks to my parrot who gnawed on it. I can zip it, but every now and then it splits open. That is not something you want to have happen when you're backpacking.
The problem with going ultralight with gear is that eventually you have honed your gear down so low that not only is it light, it's small, too.
I put all my gear back into my Osprey backpack. It all clumps down at the bottom of the pack in a big lump. There are limp and lifeless pockets everywhere. I suppose it won't hurt to have a big pack with little inside. It offends my hiker-chic sensibilities. This is silly. Fashion should not matter. Maybe I'll try my old external frame pack next.