I have fewer relevant publications than I can highlight in my application I am applying for a tenure-track position. I am allowed to add up to five particularly relevant publications. I have four first author papers and a bunch of more or less important co-authorships, nothing that directly relates to the topic of the position or were I am only one of many co-authors.
Should I just add something to the list, or stick with four papers?

A separate publication list is included.
I’d only add the four relevant ones, unless you have one that particularly speaks to your narrative about your research, etc.

The search committee can read your CV already. What they want is something they can grab onto and think about deeply, and generally I’ve found that “The applicant is a co-author in the middle of the paper” just gets it discounted.