Another one being total radio failure... You're coming back to your airfield and are about to request rejoin when you realise comms are dead. Obviously there are the no radio procedures, flying triangles etc.
I am surprised no one has pointed out that really the "fly triangles" procedure is really for someone caught above cloud so that someone can come and find you and shepherd you down, unlikely to be used much these days with modern aids, though with a transponder on 7500 it would probably be more noticeable than it would have been when first thought of!
I would also point out that if you are outside CAS and trying to get back in without being cleared to do so ideally you should remain clear and find somewhere else to land, how practical and safe this is depending on the weather and safety being overriding.