MyPackage.cs

public sealed class MyPackage : Package
{
  private DTE mdte;
  
  protected override void Initialize()
  {
    // Your package is also a service container IServiceContainer
    serviceContainer = this as IServiceContainer;
    // The DTE object contains most of the goodies you'll want to play with
    mdte = serviceContainer.GetService(typeof(SDTE))as DTE;
    // I could also add a service of my own if I wanted
    // serviceContainer.AddService(typeof(MyService), new MyService(), true);
  }
}