So. I'm using keynote to build slides for church music overheads. This means I need to build a different slide deck for each song we sing, so that we can change out the songs from week to week.
The baseline file size for a keynote presentation is about ½ MB, which is huge once you get a library of up to 40-50 presentations. And it's completely unnecessary, because all I have is simple text on a solid background.
I did a little digging, and the culprit is the default background images for slide masters that I'm not using. Eliminate these images from the package contents, and my baseline file size drops to under 100K, which is to say, reasonable.
The problem is that Keynote really wants those images to be there, and it puts up an error message every time.