you can carry multiples of everything if you want, but weapon and armor bonuses don’t stack. A great sword and dragon slayer don’t give +2 to non dragons. Chartering ship allows you to leave a location (like the ruins) to travel elsewhere (dark tower). Maybe you want to earn a little gold at an easier location before delving into the darker places, or you weren’t feeling a location that day but didn’t want to forfeit the gold and equipment you’ve earned so far.