Actually those are just coins, which can sometimes be triangular in the Forgotten Realms.
Interestingly (to me at least), the only specific example I found was the Sembian silver piece, or "hawk." In the image, we also see what looks like copper and gold, too, at the minimum.
Hm. Re-watching (scene inside the wagon starts about 1:27:00) and yeah, as she's swinging in and we see the floor from a different angle, they are flat. But at least one of them in this pic looks like a d6 with pips.