The honest breakdown
Catering ~25%, venue ~18%, photo/video ~12%, attire ~10%, music ~8%, bar ~8%, flowers ~7%, everything else ~12%. The shape holds across budgets; the levels move. Knowing the shape before the deposits protects against the category that sounds small and prices like catering (flowers, looking at you).
The regret research, summarized
Couples consistently report the same: photography and video = never regretted (the memory layer); food and bar = never regretted (the guest layer); favors, printed details, chair covers = almost always regretted (the disposable layer). The budget strategy writes itself: fund the memory layer and the guest layer; skip the disposable layer without guilt.
The upgrades worth making
Better photographer (the only purchase that appreciates), the extra bar hour (guests remember), the good DJ or band (the dance floor is the event's report card), and the video (regret asymmetry is brutal). Everything else — linens, themes, monogrammed everything — is a the-day-of detail that guests forget by dessert.