TBH I had expected your post to be about the occasions where a pre-recorded show which overruns isn't faded out correctly on the hour (most of the time it does work correctly and I found this to be a big reason why  I stayed with Airtime, as most of my content is not single tracks but pre-recorded shows around 1-2 hours).

I fill up these gaps with jingles/music beds/random sounds - as well as top of hour jingles (called "TOH jungles" on my playlist as I mistyped it first time round and then decided to preserve the misspelling so these stood out (my mind works in a strange way) I use the random items to pad out those recordings which are less than an hour long but where the gap is too short for an entire single track.

for an experimental EDM station based around house, trance and techno I've used all sorts including a old wok being struck twice with a wooden mallet for an interval signal; old gramophone records of the PTT telecom signalling protocols and a recording of a middle aged Dutchman meowing with a Siamese cat.

The idea is to add content so your show overruns slightly but where it doesn't matter if it is faded out before the end of the content. That way you should not get the dead air (which you don't want on any radio station)