Two easy answers, neither one easy to implement.
First, enforce the item slot rules. One head item, one neck item, one cloak or cape, one belt, one vest or shirt or piece of armor on the chest, one pair of bracers or bracelets, one set of gloves/gauntlets, one pair of boots, one pair of lenses or goggles, two rings.
Second, enforce the encumbrance rules. That tends to cut down on the "golf bag" issue.
The reason it's easy is because it's all already there in the rules. The reason it's hard is because it forces the players to make decisions about their items.
As for "Fashionable": A cloak can look dashing. But not if you have a backpack, as pretty much every adventurer does. (I work at a Renaissance Faire, I've seen this, it's ugly, every time.) A hat can be fashionable or plain.
The big thing, estheticly, is to know what to leave on your horse. Minimize your personal load by placing excess in your Bag of Holding or Haversack. One sword, perhaps a main gouche across the belt in back, and a dagger. A Bow is fine. Want a mace instead of the sword? Okay, no problem.
Want the long sword, the bastard sword, the two handed sword, the second long sword, the Great Axe, two shields and a Haleberd? Even if you could find a way to walk with all of that (encumbrance rules), it's going to be ugly.
So enforce a simple rule for weapons, similar to the Slot rule: One weapon on the left, one on the right, a tiny weapon in back, and perhaps a two handed weapon in hand or across the back.
Want to wear that neat looking Odachi (Japanese great sword) across the back, with the grip up over the shoulder? Looks good, but not really usable if you're also wearing a pack.
So this brings us to the ultimate fashion accessory for the stylish adventurer: Your "gentleman", a servant or second to carry all the extra weapons and hand them to you as needed. Nothing says style like a manservant in medieval societies, after all.
He carries your pack, so the cloak looks dashing, the bow or greatsword can be drawn, and you aren't encumbered by all that gear you simply must have. He is.
