Cone wrenches are one of those things that you pretty much need in the toolbox. Can’t really adjust or rebuild a hub without them, and you can’t easily find wrenches thin enough to do the job at the hardware store. Typically I’m not one to advocate cheaping out on tools when you’re purchasing them, but there are exceptions.

The pictured pair of wrenches I’ve owned for over ten years, and they’re still going strong. Bicycle Research makes some decent tools for nice prices - this pair of double ended 13/14, 15/16 wrenches are still available online for less than $10, about what I bought them from the local shop for way back when. You may need other sizes for given hubs, but these will get you started on hub maintenance.