Oh wow! I am impressed that you were able to throw away stuff like old notes. That is the sort of thing that I have the most trouble letting go of. My memory is pretty bad most of the time so those things really help me to recall feelings and memories when I look at them. But honestly I don't have much from my childhood other than my Garbage Pail Kids. I wish I had some of the notes that I passed around. so many crazy memories!
I guess as the wise say, we must live fully in the present and embrace new experience as it arises; but easily and swiftly let it go. All misery comes from attachment. At least that's what my meditation teacher says!
the notes i threw out from my middle school days were important at the time because it was our innocent way of flirting with a girl that you liked. However, when i was reading a few of them i realized that they were basically just garbage chat completely devoid of substance at all. I couldn't even tell what it was that the girl was talking about and it was just silly. They were all so repetitive that it was actually really easy to let those go.
Getting rid of the birthday cards I suppose is a bit heartless. One that i did keep had a really long and well thought out message from Grandma and she concluded her part with "I'll leave some space for Grandpa to write something" .... the rest of the card was blank because Grandpa couldn't be asked to do it. haha!