So many avenues!
In the Aftermath plotline I have an idea to use a main character who has a form of amnesia, meaning that every day he wakes up with the last memories being of a time long before any of the events of the book happen. This would allow me to write a perfectly linear account of his life post-apocalypse and the events that lead to him being a single parent but then edit it so that each day I choose to relate comes as a shock. That would be both artistic and a way for me to indulge a little. It would also allow for a deliberate confusion over what caused the apocalypse, how long ago it was and what society is actually like in the aftermath, all of which would make writing it easier. However, there is still the hang up of having to write it all in order rather than the more interesting method of how it would be read.
In the Prehistoric plotline I have an idea about following a group of male hunters from the homo sapiens tribe as they encounter a family group of Neanderthal. It is widely believed now that the Neanderthal worked in small family clan groups that would have had to have met up with other clans for breeding purposes. Evidence from my own reading mounts that homo sapiens would have had female dominated, if male led, tribes moving around as well as singular or small groups of males between them - thereby creating a less family-centric tribal system. The clash of that system alone would be interesting to write and explore were it not for the fact that I have no plot.
And then there's the one I intend to write. Currently inert and lifeless as stone. There's something in it, I know, but I can't seem to get any ideas out.