Separating "must-have" from "nice-to-have" costs early — venue, catering, and core ceremonies as essentials, with things like elaborate décor or destination elements as flexible extras — gives you a realistic floor and ceiling to plan around, rather than an open-ended number that keeps growing as planning progresses.
Wedding-specific savings, if the goal is more than a few years away, can reasonably use a mix similar to any medium-term goal: some equity exposure if there's genuinely 5+ years of runway, shifting toward FDs, RDs, or debt funds as the date approaches, to avoid market risk affecting money needed on a fixed date that can't be postponed.
It's also worth having an honest conversation within the family about who is contributing what, and when, well before the event itself — financial misalignment discovered close to the wedding date tends to create far more stress than the same conversation held calmly a year or two in advance.