[SalesForce] Can we open files/attachments in Salesforce1 without enabling Chatter

According to this post, the answer to your question about using content packs would be "no".

On the IdeaExchange you'll find a submission titled Allow Content Deliveries to be programmatically generated via Apex which has some related links on it you may also want to look at. Regardless, I believe this "idea" covers the gist of your question.

It seems to me that you might want to go and vote for this idea.

With a bit more effort, I believe I've found something in another post that you might be able to utilize the techniques from for getting a download link in it to accomplish your task. There are references to a blog post titled Salesforce: How to make a Document public? and some other useful discussion.

Based on the above referenced post, I'd say the answer to your final question is "yes". Implementation will be a matter of how you design your trigger and email template(s).

For future reference, you might find FindSF Info to be a very helpful search engine.

You can use the API to accomplish part of this. For files that are attached to feed items, you can query the FeedItem SObject for ContentData where the Type = ContentPost.

Unfortunately, files attached to comments aren't supported in the SObject API. They're supported in the Chatter REST API and Chatter in Apex, but you wouldn't be able to do a mass export because those APIs can only run as the current, logged-in user. They're not data APIs.