For men, your best business suit and the good tie. A boutineer would not be amiss, but not necessary.
For ladies, a dressy dress. Your best Easter frock is a good one, or the silk blouse and the evening wide legged slacks with the glittery belt. The "little black dress" is another option, and accessorize with the glittery accessories. If you have a "cocktail" dress, now is the time to wear it.
This is not the prom formal, so forget that dress. This is the place to wear the excellent "uptown" dress that you bought because it was beautiful...but have no place to wear it. Knee length or below...no dramatic sweeping hems. If you opt for the formal slacks, be sure to do silk or satin blouses, eye catching belts, and evening jewelry. A dramatic scarf would be appropriate too. Tasteful, my dear, tasteful always.