Just about any auto parts store will have a small plastic box of all different size fuses. Get the right type and toss it in the saddlebag. As for extra stuff, before a long trip I always make sure I have the fuses plus an assortment of crimp on connectors for temporary use(and the pliers), always have some spare wire of different size---just a couple feet of it rolled up. An extra headlight bulb and smaller turn/brake bulbs, flat repair kit and I also carry a small air pump as well. I usually will carry an extra set of flashlight batteries and extra cell phone battery if it's a replaceable item...not all cells are. In my wallet I carry a list of all the important phone numbers, usually will duplicate what's on the cell but if that's damaged in an accident you still can borrow a phone and make a call. Being a bit anal, I also will pack large items(final drive, alternator, etc.) and label what an item is prior to leaving home, show my wife where it is so if I need something shipped overnight, she can arrange for it. One year I made up a list numbered 1-5 and named each item. Then I tagged each item with the same number as on the list, made a couple copies, left one for the wife and carried one with me, in the saddlebag, etc. Then if something needed shipping, all I had to do was tell her ship item #3 or whatever you need...removed all the mystery for her. Only used that system once over 30 years ago but it saved my bacon. My wife at the time was one of those high IQ's that needed an instruction book on how to change a lightbulb. This worked foolproof.
PS: Also a few extra hand tools in addition to the kit already in the bike.
