For a casual outfit, go for a dark brown wool shirt jacket and black jeans — these two pieces go pretty good together. For a more casual take, complement this ensemble with tan leather low top sneakers. In the colder months, when functionality is critical, it can be easy to surrender to a less-than-stylish outfit. This outfit, however, is a striking example that you totally can stay toasty and remain stylish in the colder months. And if we're talking casual outfit ideas for 30-year-old guys, this combo is ideal.