C.W.
I saved my all of my favorite little dresses from my daughter, now 8, and they are hanging in my 8 month old's closet now. As for the rest of the clothes, nope. My firstborn was a spitter, so most newborn clothes got tossed. And clothes are really not that expensive, and they are handed down a lot. For newborn toys, if they aren't beat up or missing pieces and my first child liked them, then I saved them. After my first 2, it was pretty hard to meet that criteria, and most were tossed. I am sometimes sorry, because a lot of the great toys from back then are just not available now. The car seat will probably be expired by the time you have your second child, so dump that. If the portacrib worked, then save it. If you hated it, dump it and start over.
I am horrible at organization, but I had an organizer work with me. She set up "memory bins" for every family member. If the school work/art work meant something, save it in the bin. Save a few of her best pieces also. But I don't think you can save everything. My mom dumped off tons and tons of boxes when I got married. I was not happy about it. I still haven't been through them.