My favorite is: a miso base with whatever we have in the fridge. Literally. That is it. Purists may argue, but I'm not a traditionalist about my ramen. I just like soups.
My better half is vegetarian so we don't put meat in the main dish, but if I have leftover meat from some other meal, I might add slices to my bowl. Beyond that, we always have: ramen (or soba or other noodles), misos, various onions, and eggs. We usually have a few different types of dried seaweed (purple laver is my fave for soup) and veg so some of each will go in. Sometimes we'll have julienned carrots and bok choy, sometimes turnip greens and mushrooms. I usually grate some fresh ginger in there and add a little oil: plain, chili oil, or sesame. I might add Korean gochujang paste or sriracha, or any other sauce/paste that strikes me. It is a great way of making something new from leftovers.