I should add that I don't scrapbook for the most part, I'm usually making cards. I also don't plan out what I'm going to make ahead of time more than "I need to make a birthday card". That's why I have a smidge of all my ribbons & buttons with me. I never know what I might need. And I also have one of those assortment packs of basic metallic brads in my bag as well.
Oh, and inks. I buy the cube/dewdrop size for whatever inks I use and keep those in my bag. If they aren't available in that size, I make my own using uninked cubes.