Just a baking tray and magnets from the dollar store. We had number magnets. Letter magnets or pretty much any other magnets you can find would work too. There are even some downloadable activities to print and put on your trays here and here.
I set this up on an easel for her for a couple reasons:
1) It’s just easier for her to manipulate when she’s standing and facing her task.
2) Her room is small. She often ends up hanging out on her bed. Which isn’t a huge deal, but keeping the bed just for sleeping is consistent with what I suggest when I’m consulting with families.