the meaning of "bake-sale beat"?

In terms of news, a beat is an area of expertise or coverage. A reporter might be on the White House beat, on a sports beat, or on a fashion beat. A bake sale is a tiny, local event that is by no means newsworthy. So, the bake sale beat refers to minor news coverage around relatively insignificant events. You might expect to see as much coverage of this Falun Gong parade as you would expect to see of a local bake sale - that is, not much. This expression adds some flair to the text, but is really just repeating the fact from the previous sentence that there will be little press.

Etymonline gives this illumination for beat:

Meaning "regular route travelled by someone" is attested from 1731, also "a track made by animals" (1736), from the sense of the "beat" of the feet on the ground (late Old English), or perhaps that in beat the bushes to flush game (c. 1400), or beat the bounds (1560s). Extended to journalism by 1875.

(Emphasis my own.)

Either way, it's a route for some in certain professions that is routine, probably mundane, and well traveled.