||Acceptable colours for belt and shoes are black, burgundy/cordovan and various shades of darker browns. Light browns such as saddle tan and its ilk should be reserved for use with business casual wear. The belt and shoes must match one another, at the very least in colour category if not almost exactly in shade. The belt's buckle should be silver or gold. Other metallic objects worn with the suit [such as cuff links, tie bar, tie tack, watch] should match the belt buckle. Where watches are concerned, the more formal the occasion, the thinner the watch. Analogue watches are more formal than digital watches. In the most formal situations, a pocket watch, or no watch at all, should be worn.
Generally speaking, one should not wear rubber sole dress shoes, though there are some individual high end shoes that may be exceptions. Leather sole shoes are not only traditional, but more importantly they almost always have uppers that are of a far better quality and have a much more "dressy" appearance.
The use of handkerchiefs and pocket squares/silks in the upper welt [chest] pocket is a matter of taste. A general safe rule of thumb would be to match the colour of the shirt or the background colour of the tie. When in doubt, one can simply use the traditional, white cotton or linen handkerchief. There are a number of styles in which these may be folded, all at the wearer's discretion.