Actually it depends on your budget.
The senior most person of your Organisation may call a small get-together or a high tea to celebrate labour day. The idea is to celebrate individual's involvement in running an Organisation hence employees at all hierarchical levels should be called including your pantry boys.
Some of the employees especially who hard have any identity in the Organisation should be called to share their experience and then reward them with a small prize, memento followed by snacks, tea etc.
Some glimpses of the same get-together may be published on your notice board, emailed or uploaded on intranet/HRIS for others delight.