Just wanna add:
The default installation of OpenBSD gives you everything: the base system, X (xorg 7.2), a complete toolchain, and a complete man page set.
So perhaps one possibilitiy is to split up the files and put them in different partitions on different media (NAND & SD, for example). I guess this is possible, because the distribution set comes as several standalone package tarballs (you can take a look at the download locations of obsd).
The biggest trouble is up to now OpenBSD has no SD write support (a big pity, truly). But it is hoped that the final 4.2 will get SD write support, and then i am quite sure many seasoned hackers here will come up with the workarounds.