My HS828's belts lasted only 20 years, and I changed them only because I was overhauling it. I ground off rust, painted it, and when I'm that deep into a machine, I usually replace bearings and all normal wear parts. Since the bucket had to come off to get all the rust, I was into the belts area and they looked fine at their advanced age.
I've broken shear pins when the newspaper turns up in the driveway snow, so I stock the pins. Bearings and belts are available online, so I do not recommend you keep them around. I do suggest you pull the auger after a few years and put copious amounts of antiseize on the shafts to prevent parts rusting together. I check bearings after 5 - 7 years. I do have a spare spark plug on hand but only because of that overhaul (I bought two). Honda engines almost always start on the first pull...unless you feed them really bad gas.
You can get most everything you need from online Honda dealers, so why worry about stocking parts? I use boats.net for OEM stuff. The best spare part you can buy is the shop manual for your machine...and read it! Adjust the skids and scraper bar.
You would do better swapping the skids out for roller type (or plastic) and religiously doing routine maintenance. Get a can of fluid film and hose down the inside of the bucket and auger. I try to run the machine down to the end of the driveway, clean up the salty stuff thrown up by the plow, then let the rest of the snow on the driveway clean out the salt laden slush. Enjoy your machine!