If you like Kamandi, check out all the Great Disaster stories DC put out over the years. I got a collection of them, Showcase Presents: The Great Disaster: Featuring The Atomic Knights. It's cool how it puts all the stories in chronological order, but originally they were just published all over the place. But basically it's a bunch of stories after doomsday in the Kamandi timeline, but not about Kamandi. So there are a bunch of shorts called "The Day After Doomsday!" (some of which were not originally titled, many of which are just one or two pages), and they're about the survivors picking up in the immediate aftermath of World War 3. Then there is The Atomic Knights, survivors who find suits of armor which happen to have been irradiated in just the right way to make them invulnerable to the radiation which now plagues large parts of the world, as well as some ray guns that have become popular, so they use them to become heroes. Then there's Hercules Unbound, where Hercules, who has been chained up for a long time, is freed by World War 3, and goes out to do hero stuff in the post-apocalyptic world, dealing with other gods and stuff (this series actually deals with the origin of the humanoid animals from Kamandi). Also there are a few other scattered stories, like some about animal people from Kamandi stories (but Kamandi himself isn't in them), and a couple with Superman crossing over and dealing with stuff from this timeline, including meeting Hercules and The Atomic Knights. It was all really cool and I had no idea about it until I happened upon this book, despite knowing Kamandi. It probably wasn't planned to all fit together first, but once they did that Hercules Unbound series, which was after Kamandi, they realized they should put them together, and they started drawing connections.
Unfortunately I have not read that many Plastic Man solo stories, so I can't contribute that much to the actual thread topic. But I've always maintained that he's a sorely underrated member of the Justice League, and deserves to be up there with at least the second-stringers like Hawkman and Green Arrow. Also, Plastic Man of Earth-X deserved better than just being written out due to Earth-One already having a Plastic Man. Later stories on Earth 10 have done a little more with him, but it's not really the same, since Earth-X was clearly intended to be the original Plastic Man and it would have been cool to see his continuing adventures. Yes, they did specify that Earth-X is technically not the Quality Comics universe, but it was clearly intended as that when it was created, and it's cooler just to act like it is.