These are tokens I have been adding too over the last year as a way for my players to keep track of their spell slots. They're at 6th level, one is a Druid named Yulmanda, so here slots are the green ones below and Mya who was a Bard used the ones above in grey.
This last set are not presently being used at all and are really an experiment.
The first 2 sets are based on cat food box card, the grey set modeled with PVAcrete, very sturdy: the green set details were added with a glue gun.
This last set, below, were made from EVA foam, from the Range, because I wanted to see how well it would do. I like the overall effect, but the slot number details seem too high for me, so may experiment with some card for them instead. That's if I ever make another set!
Presently my favourite is the grey PVAcrete set, hard as rock they are:-)
Another thing that I made for my players earlier this year, but which I often forget to put out is this compass. I add it to a board just to indicate North. This is made from CF card(cat food card) cereal box card, PVAcrete, for the edges, and some old watch parts I got on Ebay 3 years ago.
So all these are fun to make and enhance play at the table, certainly Mrs Daxio loves them.