Hello , so cake in a jar is popular now and I had seen on Duff that he put cake leftovers in a jar. Is this ok if they are eaten that day or the next? How are they sealed, bc I thought the kids would slower come lose if not boiling hot? Could I still boil and as they are hot put the cooled cake in safely? I have seen post where cake is baked in a jar, but that's not what I'm interested in. Thank you in advance for responses if I miss anyone! Sorry about the long post!

I don't believe it's boiled. The frosting would melt if it was. And I would say same shelf life as a normal cake. Maybe longer since its in a sealed container. 

^^^ yes. I do both, bake in a jar and "pack in a jar". A bake in the jar cake with no icing can be sealed by placing the lid on top and the ring and it will "suck down" and seal as it cools--- just like jams. 

The Duff thing, is really "serve in a jar". Cute, single serve container... but just a container.