I have been doing something similar for my DC since they were little. (It's a train in their case.)
I put a small note in the drawer, telling I love them, I'm proud of them etc. Then a small gift on the top.
Depending on child it could be a pencil, or a toy car, or a pretty hair clip, bath bomb or bath toy etc.
When they were younger, max spend was a £1 per gift. I get them throughout the year and hide them so it spreads the cost. I probably spend a little more now they are older and not as excited by a toy car or fun pen or pencil.
I also alternated between the DC, so one had odd days and the other even.
I also alternated gifts, so one time it was a gift, the next time a small chocolate. So in total they had 6 gifts and 6 chocolates each.
One thing I wished I done from the start was to date the notes including the year.
If your DC keeps the notes, it's nice to remember which order they got them in. It's sweet if they keep them all in a little tin (which could also be a gift).
I have fun looking for gifts throughout the year.