A rugged style is defined by complete versatility. A rugged man’s clothing never sacrifices function for form, even if the function is a bit more subtle than what is readily apparent.
Because we live in a world where the rugged man is not as necessary as he once was, clothing has not changed as drastically. For inspiration try to find old photos of men from the turn of the century. Don’t focus on their suits or city clothing so much as their work clothes.
Look for military-inspired clothing. Things like field jackets, trench coats, earth-toned colors, and functions like epaulets or flapped pockets all originate with the military and give off a Rugged impression.
Look also for hunting-inspired clothing. Traditional hunting patterns like buffalo plaids, gun-club checks, and others are all rare these days and have a visual link to their heritage. Similar to military clothing, hunting gear was functional and the clothing had extra reinforcement in seams, close-able pockets (and more pockets), and thicker materials.
Embrace frayed edges and minor damage. These are work clothes, they don’t need to be perfect. A frayed cuff or collar gives rugged clothing some character.