It's the hard part.
My first car was a 1997 Suzuki Esteem. At the end of it's cycle it was completely retard broken and I traded it in for my Mazda6.
The Mazda6 is a much better car in almost every aspect, but I basically learned to drive in that Suzuki. I did stupid shit with it, I went everywhere with it. It was hard to let go, and it still is.
It's half a year later now, I wonder where that Suzuki is now. It definitely was the better choice, the Suzuki needed so much to be fixed in order to go again, but it stays hard.
I kept the Suzuki keyring and put it on the keys of my Mazda. It's nothing more than a simple metal plate with the Suzuki logo on it, but it's a great reminder.
I recommend keeping something of your old car as a reminder to it.