In a lot of good movie series, there are "MacGuffins' that are central objects that serve as a trigger for the plot. In the lord of the rings, it was the one ring. In Harry Potter, is was the horcruxes, in the last two Avengers films, it was the Infinity gauntlet (or, maybe the infinity stones) etc. etc. My question is: Is there a MacGuffin in Star Wars? I was thinking maybe the force is a sort-of MacGuffin (it kind of isn't though because it technically was the makeup of all nature and so it wasn't an actual thing) I mean throughout the entire series. Not each individual trilogy.
The Death Star plans/R2 when he carries the plans are the MacGuffin. They set the plot in motion and are the trigger for getting Luke involved in the story, but ultimately don't mean very much to the audience.
Using Hitchcock's definition of a MacGuffin...
"what everybody on the screen is looking for, but the audience don't care"
...then the plans are it. Lucas says R2 is the MacGuffin because he believes
"that the MacGuffin should be powerful and that the audience should care about it almost as much as the dueling heroes and villains on-screen."
So as soon as the plans are put in R2 then he becomes the MacGuffin.
Note that once everyone gets in their X-Wing at the end for the final battle, no-one in the audience is thinking about the plans anymore, even though they seemed so important before. The MacGuffin served it's purpose and got us to the end. R2 has lost his function as the MacGuffin, but we still care about him.
According to George Lucas in the commentary of Star Wars Episode IV, he claims that R2-D2 is a MacGuffin. The bit that @Todd Wilcox mentions regarding the MacGuffin needing to be, "insignificant, unimportant, or irrelevant in itself", is interpreted differently by different directors/producers so I wouldn't consider that a hard requirement on what can and can't be considered a MacGuffin.