What are common causes for Blend files growing in size? I have this blend file that seems to be growing. 



The file size is now about 250MB. It contains this scene and the texture of the flag is 265kb and the texture of the sky is 640KB. 

I have a wind blowing and I intend to render this scene as an animation. I have played the animation a couple of times and I have the feeling that this causes the growth of the file. What could be the reason for the ridiculous file size ?
In each instance the cause of growing file size may be different.

Common causes include:


Groups of objectsCause: Objects in a group might not exist in any scene.Solution: Check groups in the outliner, if you want you can add an empty scene and RMB in the outliner to instantiate all group objects in the scene to check all the objects you have in groups.
Physics cacheCause: Objects with internally stored physics cache may accumulate cache in the blend file.Solution: Clear the cache for your physics objects, you may want to use external cache files too.
Auto-packed texturesCause: Texture auto-pack is a feature, stored per-blend file, that will pack all your textures when saving.Solution: Check that you have auto-pack disabled in the menu: "File -> External Data -> Automatically pack into .blend".




feel free to suggest extras in comments - or add own answer :)