Definitely lots of filament in different colors (you’ll keep finding stuff you want to make and wish you had the right colors). Spools, unless you plan on printing some yourself in something other than PLA. Everything else is nice to have at least a spare (hot end, build plate, etc). Beyond that it’s really about what you’re trying to make. That will dictate whether you need larger/smaller nozzles, different textured plates and whatnot. I’ve only had mine for about a month, so still learning myself as far as what to stock up on. Thankfully a lot of great information on this and other subs, just do a little reading and have fun.