I personally only have the actual BizTalk items (schemas, pipelines, maps, orchestrations). And of course, the solution might also have other projects like custom external DLLs, custom pipeline components, test projects, .NET 3.X projects, all the stuff that will eventually end up in a DLLs or running in IIS.
But my question is, do you also include the binding files, strong name key files, documentation, etc. in your project? An email from a friend has prompted me to write this. I personally think that while these files definitely have to be kept in source control together with the solution files, they shouldn’t be added to the projects.