The Pipeline Utility Steps plugin provides a set of script methods that are being used in the examples such as:
findFiles to search for files by name pattern
zip to create zip archives
unzip to unzip archives
Config file provider
The Config File Provider allows defining files and storing their content within Jenkins, thus allowing you to define configuration files that do not have to be stored on disk within repository (e.g. the Git) storing the jenkinsfile.
Credentials binding plugin
Some plugins/methods, like the httpRequest, require the use of plain text credentials or tokens rather than using credential IDs as provided by the Jenkins Credentials manager. The Credentials Binding Plugin allows converting a Jenkins credentials ID into a variable containing the plain text stored in the credential definition. Thus, these plugins can be used without having to expose any plain secret texts within the code of the scripts.