Well, my preference would be to have a stuffed animal as a tangible object to literally hold onto. But she won't do that

A stuffed animal for me would be something from her that I can feel and hold when I'm struggling. She said I'll get a tangible object from her when we terminate, but it won't be a stuffed animal either.
So what I have is a letter she hand wrote me. It's a simple letter telling me to practice self-love and a quote from her favorite author. It's special because it's her writing, her hopes for me, and something that is important to her all within this single piece of paper. I also have a list that I have been adding to that lists all the ways I knows she cares for me. Lastly, I have saved every single email she has sent me. So when I miss her, I go back and read them.
She would allow me to borrow something from her office while she's gone, but she doesn't really have anything besides books and I would feel horrible if anything accidentally happened to it.
This last time she gave me something to look forward to when she was gone. I wasn't allowed to contact her by phone, but I was allowed to email. She said she would read all my emails but wouldn't respond. I asked her if she would please just email me once while she was gone. She agreed so long as she could email whenever she wanted. I agreed, and she did email me

It helped because it showed that she remembered me and that she still cared.
I think for me, I just need to know she's still there and our relationship hasn't changed. That when she comes back, she is the same person. It sounds weird, but that is why I struggle when she leaves. All aspects of reassurance helps me maintain a connection. The more I have, the more evidence I have to disprove my false thoughts about her.