Gravestone takes priority over "keep inventory" type effects.

[OJwithC]

For example, Botania's resolute ivy is supposed to let you keep the item it is applied to after death. It did not. The Witchery effect Sticky Items is also supposed to let you keep your items. It does not, the exception being items in Traveller's Gear slots, which are not caught by the gravestone anyways (not sure why the resolute ivy didn't work on travellers' gear though).