Prepare a worksheet and ask all your students to go home and gather all your information about servanthood.
Have questions for them to ask their parents or relatives about their definition of servanthood. Also, have them gather information on their parent's experiences of servanthood. How do they show servanthood? Ask for two or three experiences.
These questions can also be answered by the student's themselves. Have them give scriptural and secular references for how God views servanthood. You may give scriptural examples, but they will learn more if you show them how to find the references themselves.
The big night:
Using the information gathered, choose what kind of activities you want to do. I would prefer an outing, but if you have to do it inside, you have some very limited options. The real thing has much more of an impact than play acting. Since you got the parent's involved, then you can choose activities that involve them as well.
I like having an evening of serving at a soup kitchen. Everyone gets to talk to the homeless and poor. They serve them without expecting something in return.
A follow up:
After having your experience, have a time of follow up. How did servanthood affect relationships: between your students and those who they were showing servanthood to, and between them and God? Make sure it ties into your work with scripture and your theme.