Spell slots are one of the most complicated and tedious mechanics in 5e. A high-level spell caster might need to keep track of as many as nine different counters. That's a lot of scratch paper, or a lot of writing and erasing.

Spell Slot Cubes use a bunch of d6s or paper cubes to keep track of remaining spell slots at each level. When you cast a spell, just twist the die or cube to a lower value. When it's time to pack up, slide on the snug sheath to hold everything as it is until your next session.

Half casters, like paladins or rangers, use the smaller spell tracker with counters for spell levels 1 to 5. Full casters, like high-level clerics and wizards, use the bigger spell tracker with counters for spell levels 1 to 9.

Use some beautiful d6 dice or the paper cubes included in the set. Cubes are numbered 0 to 4 to match possible spell slot capacity.

One side of the tray is marked with the spell levels, and the other has bubbles for spell slot capacity that you fill in as you gain levels.