Well this feature is already available in Mys v1.3.0. You can set the 'target' for each each item, this defines which adoptables can use this item. The default value is 'all', which means item can be used by all adoptables. Otherwise, enter the id of the adoptables that can use this item. Here are a few examples:
PHP Code:
all => All adoptables can use
1 => Only adoptables with the id 1 can use
1, 3 => Both adoptables with id 1 and 3 can use
1, 3, 4 => Adoptables with id 1, 3 and 4 can use
no => No adoptables can use