Keynote - How do I get rid of the default background images?
So you went to your Keynote presentation document file and used the Finder to "Show Package Contents" then you deleted the image files you found in there. That would cause problems. Try this:

Open a new Keynote document and select the Theme that you want to use as the basis for your presentation. Now do...


View -&gt; Edit Master Slides
Delete all Master Slides that you don't need.
If you need a Master Slide with an image, replace the image with a small place holder image. For example, a JPG file with a solid color. 
Remove the Back Ground Image from All Remaining master slides, and remove any other unneeded elements from the slides.
Click the Done button at the bottom of the Master Slide editing screen
File -&gt; Reduce File Size (which will probably do nothing)
File -&gt; Save Theme...
Give it a name such as "Church Music"


Now you can create a new presentation using the "Church Music" theme. Your theme will be on the "My Themes" tab of the theme browser. After you save, you can now view the presentation's Package Contents to make sure that there is no unused items. Keynote will generate a variety of slide previews and other images which you need to keep, but these should be very small. If there is stuff that you really don't need, you might try re-editing the Themes Master Slides.