Hi Matt,
When you create an asset bundle using something like this:
tk2dSpriteCollectionData data;
BuildPipeline.BuildAssetBundle(data, new Object[] { data }, path, BuildAssetBundleOptions.CompleteAssets | BuildAssetBundleOptions.CollectDependencies);
The dependencies will automatically be collected. The texture & material are dependencies of the sprite collection and as such, will automatically be included in the asset bundle without you explicitly telling it to.
Asset bundle compression is really really good - I had a sprite collection with an 1024x512 atlas compress down to 32k.