A decoration worn over the top shirt button, usually with a mandarin-style collar.
An ornamental device that fits through the buttonholes on the cuffs of a French-cuffed shirt to hold the cuff together.
A wide satin band worn around the waist with a tuxedo. The cummerbund usually matches the bow tie.
Braces are what suspenders are called in the world of formalwear. Belts are almost never worn with formalwear.
The vest that is worn under the formal coat. It covers the beltline of the trousers. The waistcoat has become a popular option, and the variety of colors and fabrics available make it a great way to personalize the ensemble.