Well, it depends on your skills and what kind of portfolio your clients ask for. I can share some comments if you are a content strategist, UX engineer, or a technical communicator. You can prepare custom portfolio, such as content inventory or gap analysis, or a quick guide from whatever apps you use in routine.

For example:

(a) If you blog, prepare an ‘inventory’ of how you planned this blog, your branding process, and calendar (if any).

(b) If you manage any facebook or G+ brand page, prepare a quick guide to share how you post media, moderate the page, and see insights and analytics.

(c) You can prepare a story of how you plan and structure your resume (digital or paper), the conventions and styling, and the branding.

(d) Prepare a UX report for gap analysis and optimization scope, for any app you use (ToDo, Emails or for anything).

I always recommend NOT to use your portfolio from past employers. Create your own custom portfolio, and show the value.

Need more directions? I can discuss more on a call.