I'd call the doohickey, upgraded fuses and t-vent on the carb essential. For me, pannier racks and engine protectors are equally essential (but others differ). Some sort of seat add-on was necessary for the sake of my sorry butt after about 25,000 miles, but this need not be a custom seat--I use an Airhawk, others do with sheepskin or gel pads. Better pegs are sure nice if you don't like sliding off whenever they get wet....but that might necessitate changing out the shift lever.
Lots of people put the springs, front and rear, or cartridge emulators and upgraded shocks, or all sorts of other stuff, in the essential column. I don't, but you can search for these threads easily enough and make your own decisions. Some claim to need different windshields, some find it necessary to move the license plate, add better lighting, modify fuel mix and/or jetting, etc. etc. etc. There's a lot which you might or might not define as "a waste of money," depending. Make your own decisions.
Hope that helps.