The main thing I have to show for the last couple days, sad to say, is a two-page chart in tiny handwriting of all of the plot developments in the first novel, with loose ends and mystery back-story marked in various colors:

(I used the camera for that one, as it gives a better sense of the 11"x15" watercolor pad I purchased the other day for precisely this purpose; the scanner images below are probably more legible.)
I had a couple stages of chart-making when I was writing the first book - this was a preliminary map of the whole plot:
And this was a reconfigured version once I had a clearer sense of what needed to happen in the second half of the book, which was largely a blank when I began (barring Sophie's discovery of zombiefied girls at IRYLNS and the dynamite factory showdown):
I am contemplating introducing epistolary interruptions into the sequel, but it remains to be seen whether I can find the right voice for the letters I envisage - I suddenly wonder whether I could turn the whole thing into a kind of pastiche of letters and documents? But no, perhaps that is not really the right idea...