In your email you can easily link to your other Google products by clicking on the apps icon to the right of the search box. This icon is a 3 by 3 grid of boxes. If you are using an Android device you will notice the apps icon is the same.

Link to Drive

Clicking on the apps icon reveals a grid of Google products that you can quickly link to. Google Calendar and Google Drive are my two most used apps. Click on the Drive icon to open Google Drive in a second tab.