Full Google Support Article at https://support.google.com/chromebook/answer/3214688?hl=en
Even if you’re not connected to the Internet, you can still do lots of things with your Chromebook.
Note: Some offline apps and services won’t work in incognito or guest mode.
You can read, respond to, and search your emails when you aren’t connected to the Internet using Gmail Offline. To set it up:
Once you've set up offline email, you can use it by clicking the Gmail Offline app .
Any messages you write, archive, label, or delete while you’re offline will be sent or moved when you connect to the Internet. Learn more about using Gmail offline.
You can see your calendar and respond to event invitations while you’re offline. First, turn on Google Calendar offline:
To see your calendar when you’re not connected to the Internet, open the Google Calendar app . Learn more about using Google Calendar offline.
Watch movies and TV shows offline
Listen to music offline
Play games offline
You can take notes offline using Google Keep. First, if you’ve already taken notes, you’ll need to save them so you can read and edit offline:
After your Chromebook saves your notes, you can edit them or write new notes offline. Any changes you make will show up in Google Keep the next time you’re online.