an eidolon can be equipped with a bag of holding? or are unable to travel to the plane of eidolon when he is called off? and the rest of the equipment? swords, magic and other objects?
This is a grey area that's existed for way too long, but there are no rules stating what happens to an eidolon's items when he is dismissed. It's up to your DM whether items go with it or whether they drop to the ground.
Edit: I don't see why the bag should be treated any different from any other item though. The eidolon lives on another plane, not in an extra-dimensional space.