Under Configurations -> Drop down lists -> Activities you can create the drop down options for Activity Actions. This is a single option drop down list.
Examples would be:
Send email
Send suggestion
Arrange meeting
Send SMS
Other
The lists can contain maximum 400 lines with a maximum 50 characters per line.
WARNING: if you have existing live data in the system, then editing Drop down lists could affect your data.
If you want to create or edit tags to your activity log, you click on History log under Drop down lists. Here you can create or edit your Event tags:
Then you will be able to choose them in your activity log