Passing value from one activity to another in Workflow ?

[peterg157]

How to pass values from one activity to another in a workflow ?

[Abhinay Erra · Accepted solution]

Use workflow scratchpad to pass the values across the workflow. Go thru section 6

Using Variables in a Workflow - ServiceNow Wiki

[Chuck Tomasi]

Try using the workflow scratchpad.

Using the Workflow Scratchpad - ServiceNow Wiki

If you are creating your own activities, you can use inputs and outputs and use it more like a data bus.

[Tim Woodruff]

It appears that this does not work inside of custom WF activities. 
For example, I'm trying to set a workflow scratchpad variable in one custom WF activity, which needs to be passed into or available to the next workflow activity. However, it throws the error: "workflow is not defined". 

This isn't documented anywhere, and I don't know how else I can pass data from one custom WF activity to another.