First of all, you're very eloquent and have a wonderful way of expressing yourself. Cherish it - it's quite a gift.
You obviously feel that you should be doing something with the things she gave you, otherwise you wouldn't be at this crossroads. I say look over the things and keep some for now. You don't need to keep everything in order to still honour the part she's played in your life.
As others have mentioned, she's been a part of you for a great many years. And she always will be, because she has helped to shape the person you've become. And from what I can, that's a really fantastic person.
I've been, well I haven't been in her shoes completely because I didn't resort to the drugs and alcohol. I easily could have, but my escape was reading. I think that while there are a great many commonalities between abused males and females, there are some things that are specific to girls. So having been on (wait, that doesn't sound right) here's my advice to you:
Sarah was not ready for a real relationship with you. She probably wanted one, and I'm sure part of her desperately needed one, but she needed to heal first. I remember being a teenager. I was remarkably mature for my age, and I thought I was ready for love. And I was, but not from someone else. Whenever a relationship got to the point where he would say "I love you" (which happens real quick at 16) I would panic and shut down. I wanted love. I wanted to be married, and to have the perfect life and the perfect husband and raise perfect children and have a completely different life. But I knew I couldn't do it. I wasn't perfect, and you can't have a perfect relationship when you're broken. Sarah is broken, and she needs fixing. And only she can do it. You can try and help her all you want, and it's not going to make one lick of difference.
It's like trying to make someone quit smoking. You can hide the cigs, you can crush them, you can drown them, and they'll still find a way to do it. They'll only quit when they're ready to, and not before. It's the same with Sarah. At some point, hopefully, something inside her will snap into place and she will realize that she is worth more than she thinks she is.
Sarah doesn't think you're not good enough for her. Sarah thinks she's not good enough for you. And the truth is, that no matter how nice, or sweet, or smart she is, she's not really going to be able to love anyone truly until she learns to love herself.
Keep some of the items. Regard them the same way you would mementos from a vacation. These are postcards from your life. It's the "been there" pile. You need to remember where you've been, either so that you can go there again someday (even if it's with someone else) or avoid going there again.