Google Spreadsheet has Autofill feature similar to Microsoft Excel but with some limitations. If you want to see an example of Auto fill number series then type 1, 2 and select the values as shown below.
When you hover around the square dot, a plus sign would appear. Now drag the plus sign down to generate auto numbers.
Similarly you can Autofill month names or names of days in a week etc.
Autofill feature in Google Spreadsheet can also get data from Google Sets. Google Sets can automatically create sets based on couple of examples. If you type in red, blue and then drag down the + sign by holding Ctrl key on Windows or Options key on Mac then the color list would be automatically generated. Also shown below is an example of London sights that has been generated automatically after entering the first few places.
For more on Google Sets, check out this link