Merge all layers. Layers > Merge > Merge All
With the Selection Tool, make a Custom Selection.
Now crop: Image > Crop To Selection
Just where to crop a pattern so it will repeat seamlessly can take some experimentation before it looks 'right'. There are tools and plug-ins that will help you make seamless tiles, but I prefer to do it manually, especially with a simple pattern like this one.
Test your 'seamless' pattern by opening new image 400x400 and flood filling it with the Cookbook Chex pattern tile. The fill should be a perfect repeat of the pattern with no detectable seams.
Important: In the Material dialog box, change the Angle back to 0, the scale to 100, and be sure to UNcheck the texture box!
SAVE your new pattern tile to use as a background pattern or to fill text or other designs.
