In my contracts I specifiy ownership. Client owns the footage and final project, they paid for it. I am allowed to use any of it that I want for demo or promotional purposes. I own any avid projects, ae or photoshop files, etc. If there is music licenses or items with time limits I let the client know about them and leave it at that.
I rarely had over master tapes, I’ve rarely been asked, but if I do I clone them first. Ther was one time where I cancelled a clients contract and sent them their shoot tapes with making copies since I intended to never work for them again.