I’ve released a small solution on CodePlex for CRM 2013 online and on-premise which adds a new command bar button to the opportunities entity which will allow you to perform a lookup of another opportunity and to copy the line items from that opportunity to the current one.
I’ve released the solution on CodePlex to enable others to hopefully learn from what I’ve done, anybody is free to look through the source files or to use the Managed Solution in a private or workplace deployment of CRM. However if you use the source code for another project please link back or credit the blog.
I’m also considering creating a short tutorial series on creating your first CRM solution which will hopefully cover setting up a new solution, retrieving basic information from linked records, setting different field types, creating a custom button and hiding that button based on permissions among other things.
So be sure to comment if there’s anything else that would be useful for me to cover.