Reddit mentions of Fidget Toy, Stress Ball, Stainless Steel Chainmail Vortex

A fidget toy might be nice! After looking around, I got one of the vortex balls, because it seems like it would be weighty, fun to play with, and less likely to run away from me than one of the slidey/foldy ring toys... though I caved and got one of those too!

If you do decide to go with one of the vortex balls, check whether you're getting aluminum or stainless steel. That's a detail I only noticed as I was fetching the link, and I had a moment of alarm because I was afraid I got the aluminum one. (I want mine to be heavy.)

Assuming the comments are trustworthy, people really seem to like this seller, and they appear to be genuinely hand-made, too, for what it is worth. The vortex ball also comes in all sorts of colors and could be seen as decorative, too!

Also, I like the idea of the Tile -- tech is fun, and that is supremely useful! I might stay away from the planner and instead get a giftcard to someplace. That is speaking as someone with er... attachment issues with office supplies. Your friend might not be as picky as I am though, so it's just a thought.

You might also get them a dot-gridded journal, like this or this (I've also heard great things about Leuchtturm notebooks, but they are more expensive and I don't have experience with them) -- and then put a post-it note on the cover with www.bulletjournal.com written on it. ADHD-ers tend to love that journal system, at least for a good while, and it is extremely flexible, customizable, and not specific to the notebook you use. (Though the dot-grid allows for the best of a clean appearance and straight lines.) So no concern about planner incompatibility -- and no concern about mourning the waste of a dated planner that was never used. (hangs head for a moment of guilty silence)

For post-its, I enjoy the full adhesive ones, since they can be used for labels and all sorts of things, without a flappy nonadhesive edge (when I am really in a mood, I'll snip off the very narrow nonadhesive edge on these -- and they can also be cut into smaller pieces for smaller labels). You might be better looking in a local office supply store, though -- the colors on Amazon are not always the colors you end up with. (sour look)

Anyhow, hope this helps!