Currently the Lead Conversion functionality does not automatically attach the Activities, Messages or Files to the Opportunity created during the lead conversion.  My sales users have been complaining about this for a while and it doesn't seem like the current functionality is going to change for a while.

Has anyone built anything out to fix a similar issue or have any ideas to handle this request? 

My initial plan is to create a script that will get the Activities that were attached to the Lead and set the Transaction field to connect them to the new Opportunity.  I'm not sure how to handle the Messages or if that's even possible. If I can't move the Message then I am thinking about creating duplicate message as an activity and put it on the Opportunity.