The weapon Arya shows Gendry appears to be a two-part dagger-spear-staff hybrid. It’s got a pointy end (and we all know Arya knows how to use that), but then it’s also got a detachable bottom that can be removed for... something. From the quick look we get at it, it’s either so Arya can use it in close quarters for hand-to-hand combat, or so it can be put on some sort of longer spear so she can fight people from far away. It should also be noted that the blade appears to be shaded in black and labeled as dragonglass (screengrab here) which could point to it being the only necessity that Arya's current arsenal is missing.