A waistcoat and jeans are absolute essentials if you're planning a classic and casual wardrobe that matches up to the highest sartorial standards. For a truly modern hi/low mix, throw dark brown leather brogue boots in the mix. A no-brainer pairing appropriate for 20-year-old men who prefer to dress more elegantly.
Such pieces as a waistcoat and jeans are an easy way to inject some rugged elegance into your current outfit choices. When not sure about what to wear in the shoe department, introduce a pair of dark brown leather chelsea boots to the equation. Your twenties is a great decade to dress smart. And it's easy with examples like this.