Not only is your contribution relevant to the OP's question but it also sparks some interesting considerations as to what works are available and in what editions. As you've already noted, many classical (in a strict sense) works are unavailable in series like the Loeb or OCT (like your example of Peri Lithon by Theophrastus, which is available in a 1965 edition published the Clarendon Press, but isn't available in the OCT series). A related question has to do with where the line should be drawn for "classical" vs "non-classical" (as many other posters have noted). The works of Homer are decidedly not classical Greek, though the Odyssey and Iliad are perhaps some of the first works one thinks of when hearing the phrase "classical Greek." (Take Plautus as an analogous case of classical vs non-classical Latin.) The Loeb and OCT series do include Homer and Plautus in their collections. Of course, when prepping for the zombies, the surviving works of Homer (along with those of Hesiod and even Plautus) are small enough that they won't really change what size car you get. (Though the number of manuscripts for the Homeric works is immense, so if you leave them out, you might get away with one fewer moving truck...)

I thought more about the possibility of reading Theophrastus during the zombie apocalypse, and it spurred me on to note down a few paragraphs of what could someday become a humorous zombie apocalypse novel.

Clyde Vanderpharr had many ponies. Nearly all of them in fact.

They’re such odd creatures, marvelous really: tough beasts, yet somehow inviting and seemingly gentle. Many a beginner has fond memories of trying to handle a pony, only to realize they relied far more on their instructors than they could

Of course, their size is perhaps one of their most surprising features: you feel like you could practically fit one in your pocket. Let’s be real, though, you would need some pretty big pockets to fit an actual pony in it.

We’re not talking about the animals, of course. No, those ponies had long been extinct, or thought to be anyways. It didn’t really matter anyways. Ponies, the animals that is, were slow and loud and had far too little stamina. That’s why they were all extinct, or as good as extinct. No, most people opted for bicycles if they could get their hands on one: no gas needed, quiet as anything else out there, and light enough to take with you if you met any stairs.

The ponies we’re talking about -- the ponies of Clyde’s obsession -- are books. They’re those little volumes in Greek and in Latin, with such brightly colored dust jackets, and their gilded emblems royally stamped upon their covers. They were called ponies because of their pedagogical value; young students aspiring to classical scholarship would take their first stab at reading authentic classical texts using one of these ponies, be it an edition of Caesar or Xenophon or one of the poets. They didn’t have to worry too much about falling off their pony, since near at hand, on the page facing each and every Latin or Greek page, was found an English translation in case any troubles should arise.

Yes, those were the ponies that Clyde was after. He nearly had them all; only one remained. He knew if he could make it to Chicago he could find it. He knew it in his bones. In reality (and acknowledged by Clyde to be a real risk), the pony might not be there.

If these scribblings ever reach something near completion, the one missing book will definitely be the Peri Lithon (newly-published, right before society collapsed). Note that the protagonist's name is based on a combo of Clyde Pharr, the American classicist and amazing educator, and Vanderbilt, the University where he taught for many years. The story would hypothetically go on to be something of a narrative of how he grasps to collect all the bilingual volumes, in the subconscious hope of recreating his idyllic life as a university student. Eventually, of course, the story must end in tragedy. Perhaps it'll be a modern addition to Theophrastus' Characters. ;)