We don't need anything other than Zazen, any of those trappings. In fact, they are no big deal, of no importance, when we drop all viewpoints in sitting Zazen. Pursue your own Practice. Ultimately in Zazen, we sit with ourself and ourself alone (literally, with our "self"), and wrappings, bells and whistles are a sideshow. Ultimately, it is a matter of you exploring and sitting with your own "me myself and I" This practice is not limited to any place or time ... we drop all thought of place and time. It certainly is not Indian, Chinese, Japanese, French, Namibian or American
On the other hand, we have to do something, to greet each other somehow, read some words, dress some way. Why not do such things? As I often say, for example, we have to do something with our hands when practicing 'walking Zazen' (Kinhin) ... why not hold them in the traditional manner of Shashu (I mean, better than sticking 'em in your pockets)?
As well, there are parts of our practice which we do BECAUSE we resist (for example, when visiting a temple for Retreat, I usually put my heart fully into ceremonies and arcane rituals BECAUSE I resist and think some of it silly or old fashioned). Ask yourself where that kind of resistance is to be found (here's a clue, and it is right behind your own eyes).
What is more, there is method to the madness, and many (not all) customs have centuries of time tested benefits ... embody subtle perspectives ... that support and nurture Zazen Practice at the core. Many parts of our Practice, though "exotic", are worth keeping, even if they strike someone as strange at first. Bowing, statues, rigid decorum in the Zen Hall and, yes, weird talks about Koans all fit in that category. They may seem like unnecessary "Japanese" or "Esoteric" elements at first, until you understand the role they serve.