Here in NY State, students have to complete a certain number of labs with passing grades in order to sit for the state final exams in science (required for graduation). In other words, that lab qualification is their first step toward what they need to graduate.
Also, students usually can't go to summer school unless they have completed their labs. They can retake for course credit, and sit for the exam in the summer, but usually can't complete labs.
Whatever your pedagogical thoughts about required labs, and, coherency with the course, etc., getting 'lab qualified' is a big deal.
I always make a display or do a pizza, or do some kind of recognition. This year, since I didn't have my own classroom, I did a display in the hallway. I made a big banner (included as a freebie), got foam stars from Dollar Tree, and let kids write on their stars and hang them up when they had met the lab requirement.
It was a big deal because it was in the hallway. Some students would stay after school to make up labs and then ask me right away for their star, or ask to wait and be recognized in class.
I'm sure there are many things that you could congratulate your students on. If you don't want the banner to be HUGE, you can print two pages per page and make it a bit more manageable.