I think the Crossbow Sling from DF1 is a seriously underlooked item. At least in my games.
It's pretty cheap - $200.
It's light - only 2 lbs!
And it lets you carry a loaded crossbow hands-free, a Ready action away from firing. And it keeps it from breaking on a drop (since it just re-slings away from your hands.)
Way back in Man-to-Man, our favorite purchase was a high-ST crossbow and a single quarrel. You'd walk into the fight with it out, take a single shot, hoping for a disabling hit. Then you'd drop it and melee since it took too damn long to reload.
Players did that in my fantasy games, too, risking breakage from dropping the crossbow. They'd deal with loading and reloading it daily, the worries of dropping the bolt or securing it in place.
But the crossbow sling turns the $150/6 lbs one-shot weapon in to a $350/8 lbs weapon that's ready to hand when you need it. And if you have a really strong friend, you don't need a heavy windlass to re-load it. It's just "pass it over to the Barbarian." So you just need to get one barely able to be loaded by your friend, sling it, and Ready it when you need to take the shot, then drop it as a free action. With a typical DF party, ST 21-22 isn't even slightly unreasonable, and a ST 22 crossbow does 2d+4 impale . . . more with poison.
Yes, it's mostly a big ridiculous, but hey, you're going into tunnels to kill monsters, you have to expect some silliness.
And yet it doesn't get used too much in my games.
Perhaps until after right now when my players read this and buy them in bunches.
Any equipment you think is awesome but overlooked in play?