Summarize the thesis, preferably in prose form, from the perspective of everything that was discussed in the document
Summarize the contributions. Here it can be either general contributions or chapter-by-chapter; however, I already have a section with chapter-by-chapter contributions, so I would also go for a prose form discussion
Describe the software/data you presented and how to use it
Discuss on future work you'd like to do, or you'd like to see in the field
Most PhDs spent more text here than anywhere else of the conclusions
One section per subject is a popular way of organizing this
Closing conclusion (I liked that closing paragraph from Hankinson 2014)
I drafted a layout of my conclusions chapter, but I am not sure of what else to write. Looking at previous theses to grab some inspiration.