I believe you want to get married, and already know that there has to be some kind of ceremony in order to get married.
You characterise her desires as wasteful, meaningless, showing off and just worrying about what other people think.
You characterise your desires as useful- buying furniture or a nice car.
The issue here is about values, and a major difference between you that will, if not resolved, break your happiness together. Have you been together for long? I ask as I'm surprised that this difference in values has not come to light before, as it seems so extreme.
Your relationship will not survive long-term unless you can communicate as adults about these basic issues. Sadly, you have each taken up opposite and conflicting positions about something that is intended, by it's very nature, to bring you together- MARRIAGE. I guess you see the irony here.
So, you've asked the question- what are you going to do about it?