This is a very hard thing to do. I will speak from the other side. The side that was left with 20 years of mostly everything, my MLCER having only actually taken MY Aeron chair, MY cast iron frying pans, MY pancake turner/spatula, a bunch of random food and sundries and his car. I had to bag up or force out everything else that was his and get my chair and frying pans back (they belonged to one grandmother each, so I wasn't giving them up-I traded them for HIS two frying pans). Most of what we owned I had purchased before we got married and in the case of the couch and loveseat, recovered (I only buy quality because I expect it to last my lifetime). I was still willing to let him have half, but he really didn't want to take much of anything. I still have all the swords.
Make sure you get: Any shot records, birth certificates, passports, important papers. Yours and your children's (even if only a copy of theirs)
Any insurance papers, wills, trust papers, bank account information, retirement information. Imagine there was a fire, other than your family, what would you take? Take that. (I keep mine all in one box)
Any family pictures or copies of pictures that you would like to keep (I have good memories that are real, no matter what my MLCer says)
Any mementos, like gifts your children have given you.
Your half/portion of whatever favorite or sentimental cooking utensils you have (some things don't matter, others do--I had a set of Revere ware pans that were mine and given to me by a grandmother. The other pans didn't matter)
Check wall hangings and photos, make sure you get your half of anything favorite or sentimental.
Tools. You will need your half of the tools at some point.
Spare keys to a car or house or shed, if you need them.
Anything that is specifically yours (hobby supplies, computer, flashdrives, tablets, etc)
If you have a yard, make sure there is nothing there you want. My mother had two matching concrete lions I loved that got sold because I didn't look in her yard until too late.
If you aren't sure, and are afraid she will toss something, box it, date it and label it and take it to your new place. Stacking boxes in the closet for a temporary time isn't terrible as long as you come back to it and decide if you still want it.
Don't assume she wants something. If you want it, ask for it. If you decide to let her have it, ask her to please let you know if she decides she doesn't want it anymore.
As I went through the house, I found that paper items could be scanned and tossed. I only wanted one comforter out of the three that were left. I had no use for any of his clothes he left behind. I got rid of brewing supplies, books I didn't want, canned food I never liked, sheets of wood that were too thin, chairs that didn't fit me, video tapes, a very broken down wood playset, scraps of things I didn't even know what they were . You will likely be leaving many things behind you do not care about. But don't leave it behind assuming it will just stay there. It might not.
What I got new for me:
A bed
Sheets in my favorite colors
A reclining chair for the family room
A massage chair (I so love that thing)
Set up a craft room
There is still much more for me to remove. I put some of it out every week with a FREE sign, for those who have less than I do. The monetary value isn't always worth as much as the appreciation from someone who needs the item.
Take what will make you content. Leave what feels right. Help remove anything neither need or want. If it all works out and you get back together, cleaner is just fine. JMO.