Several readers came through with the explanation for the appearance of this strange message (as mentioned yesterday). The phrase "Bluets and Granola Bars" can be found (by using ResEdit) in the System file's DSAT 0 resource; it's where the phrase "Welcome to Macintosh" used to be. There is an additional phrase there that says "make a chewy snack," although this does not appear on the screen with the Granola phrase. You can also see the message (more easily) by using the utility, Errditor, which displays System file messages.
The message is surely some sort of joke. Mac OS 7.6 eliminates the "Welcome to Macintosh" message that has been standard on all previous system software versions - replacing it with a Mac OS splash screen. I have been told by someone at Apple that this was actually quite a slick trick to do, as the basic call is in ROM and (as it occurs very early in the startup sequence) is normally accessed before the system software could change anything. I guess after making this change, some programmer figured that the Welcome to Macintosh text was no longer needed and so they changed it. However, the text appears to reassert itself in certain situations.