The formula for a neat casual outfit for men? A navy field jacket with blue jeans. You could perhaps get a little creative in the footwear department and complete your getup with a pair of dark brown leather casual boots. So when summer is fading away and autumn is setting in, you'll find this ensemble to be your everything. As you go into your 30s, you probably want to start dressing more like a mature gentleman. In this case, looks like this come in very useful.