In reply to here_for_information.

I personally use 4 x 6" index cards, though I could imagine that many might prefer 3 x 5" cards. I have purchased index cards from Amazon before, but they're also readily available in variety at most office supply stores, general goods stores (Target, Walmart, and drug stores), and many stationers online.

As for boxes, you can go with an inexpensive shoe box to start, but the sky is the limit. Try https://boffosocko.com/2022/12/26/the-ultimate-guide-to-zettelkasten-index-card-storage/ for ideas if you need them as well as places to look for them. You can get some really great wooden boxes for about the same price as some of the prefab cardboard boxes.

Cards, a box, and a writing instrument of your choice and you should be good to go. Everything else is icing on the cake.