I have a few variations and depending on my mood will use the following:
dashi, soy sauce, sesame oil, sesame seeds, katsuo bushi
Also, I rarely use spinach (too expensive in Japan) and instead lean towards other greens. Explore and see what you like. Shungiku (chrysanthemum greens), bok choy, any thing green and leafy. Also, chrysanthemum flowers are also great in the ohitashi style.