I have a 5"X7" manila envelope addressed to me, in my mom's handwriting, mailed when we lived in PA in 1999. I use it to store the unpaid bills (I sit down at the end of the month and schedule all payments at one time). My mom died in 2005, so I like having this keepsake. I have taped the envelope seams several times to keep it intact, but her writing is still on it, undisturbed.
I also have a scrap of paper listing all my paternal aunts and uncles, by first and middle name. It's written in my dad's handwriting. They've all died now, so it's nice to have this. They also had a lot of nicknames (like Uncle Gilly) so it's nice to really know who is who! I also have the letter my dad wrote to my mom on the night of my birth (I'm the first child) as well as some anniversary, birthday, etc cards he gave her.
I have a letter hand-written by a neighbor that was sent to my mom when he learned that my father had died. This neighbor, who was only 19, was stationed in Viet Nam at the time.