I have gotten lots of use out of the content generator plugin. It allows you to quickly fake users and profiles directly from Sketch. It pulls data from:
This allows you to mock out realistic prototypes easily.
Subtle Patterns

I really like the collection of patterns by Subtle Patterns. They are amazing for simple backgrounds that don’t distract the eye but are very pleasant and provide a real quality.
I thought it would be useful to pull these directly into Sketch so I made it into a plugin. It is available here.
Usage

- Select Shapes +
Plugins > Menu > sketch-subtlepatterns > random - Wait for the image inserted as a fill
Installation
Official documentation is here.
Clone
- Find Sketch Plugins folder using
Plugins menu > Reveal Plugins Folder- E.g.
git clone /Users/dunc/Library/Containers/com.bohemiancoding.sketch3/Data/Library/Application\ Support/com.bohemiancoding.sketch3/Plugins - Download the ZIP
- Unzip and put into Sketch plugins folder