Rigify: picking an object

Hi, I’ve got a question.

I am using rigify and I haven’t found the way to parent an object on the go. How can I parent an object as a child of a rigify bone? If this is not possible, can you tell me another way to pick up objects using rigify?

I have read there is a parent modifier but I am making animations to use them in Unity but I was said that these reparenting modifiers cannot imported properly within Unity.

Thanks in advance, any suggestion will be appreciated.