I have a small (pocket sized) stone which, with practice, can sharpen anything. I have some scandi and flat ground (single bevel) and double bevel knives, as well as convex blades, all are OK. Axe too !

For a while I was using some sandpaper sheets mounted on a sheet of ply, as recommended on many sites, but I didn't like that, so I went back to the stone - like Byrd_Huntr mentions and pictures.

The custom gadgets for sharpening certainly are very popular and some are very good on all accounts, but to me they seem a bit overly fussy and some are quite expensive. The KISS principal for a simple and effective stone cannot be overstated IMO.



Hope its Ok to mention this ?
If you do a search for something like "Ray Mears sharpening knife" you will find a few nice videos demonstrating the technique (no affiliation to Ray etc on my part).