Page-
I attach more sentimental value to things as well - I haven't thrown away my son's first Happy Meal toy because it has a sentiment.
Let yourself grieve the loss of the item, perhaps even write about it so you always have the memory. That's what the sentiment is for afterall - the memory of something and someone special.
You are correct that they are just "things". Going through chemo a few years ago really taught me the value of the people in our lives, but things can help with the memories of those people and how we felt.
Some people (my husband being one) have no sentimental attachment to anything. he also doesn't remember what he wanted to be when he was a child (what he wanted to become when he grew up). He has few memories of his childhood because there isn't any sentiment.
Just like anything or anyone else, no one can tell you how to cope with the loss of something important.
Good luck getting past it.