When a player is killed by a giant spider and leaves bones, there will be a web trap placed on their square, and occasionally one or two giant spider eggs.

Bones of tortle players contain a tortle shell, which is useless except as an indicator the dead player was a tortle, or as polyfodder.

Items in a bones pile, in addition to being cursed, could be subject to additional degradation such as erosion, loss of magical charges, or blanking. (Though since a new player will arrive in the bones level apparently immediately after the death, it could be a bit of a stretch to have the items degrade so much.)

Internally mark all of your starting gear with a special flag; if you die before receiving the quest, any items marked with this flag get degraded when placed into your bones pile: things like magical armor becoming nonmagical, wands lose charges, scrolls may fade, and spellbooks are made too faint to read more than once.