Klaus pointed out that there are two problems that keep git-annex from being used on USB keys, that would typically be VFAT formatted:

  • Use of symlinks, which VFAT does not support. Very hard to fix. Instead, just use bare repositories on the key, they're supported now.
  • Use of ":" in filenames of object files, also not supported. Could easily be fixed by reorganizing the object directory.

Done; in annex.version 2 repos, colons are entirely avoided in filenames. So a bare git clone can be put on VFAT, and git-annex used to move stuff --to and --from it, for sneakernet.