Check whose time, money or access would change
Buying a table raises several different questions. Does the price come from shared money? Will the table use space someone needs for another purpose? Must another adult help collect it? Someone can like the table and still be unable to promise a Saturday collection. Ask separately about the shared effects rather than treating enthusiasm about the object as agreement to every cost and duty attached to it.
Set boundaries for the choices that recur
Agree on a simple boundary for recurring choices. Either partner might replace routine supplies within an agreed amount, while a new commitment of time or money needs both people. Revisit the boundary when circumstances change instead of arguing over each individual purchase.
Leave individual choices with the person making them
A weekly evening class is a personal choice until it requires someone else to do dinner, pickup, or bedtime. The household can agree on coverage for Thursday evenings while leaving the class itself to the person attending. If the class later adds Saturdays, reopen just the coverage question. This gives people control over their own interests while making the work or resource they ask of others an explicit decision.