With 1 child, I could keep everything in a large 3-ring binder and page protectors. THEN, my parents dropped off boxes that they had kept for me, full of art from K-3. The paper had been eaten by various bugs and feces from those bugs deposited in that box. Anything that was previous food, like macaroni art was GONE and yep, more feces. I was so grossed out that I had to go through feces and bug carcases, that I threw everything out....and had very few memories.
NOW, I scan everything and put them as full pages (or partial pages) in a scrapbook on www.mixbook.com and when the year is up, I have it printed and sent to me, so I have a hard copy AND it's online, so if the house burns down, flood, earthquake, etc, I can always order another one. (I also do this will ALL birthday cards, Valentine cards, etc.)
I can't imagine keeing everything with 3 kids and another on the way...adn they love it since they get to see their art each and every time they pull their "big books" out to look at. Nothing ever was looked at when it was in a plastic bin of keepsakes.