I think that integrating cooperative activities where students must work together and individual sports, such as golf, or possibly tennis are all units that woud work with class sizes in the single digits. Creativity would be the key, but switching activities frequently would be necessary to keep the students engaged.

You can do a fitness/cardio circuit with the smaller groups. You can use stabilty balls,steps with aerobics, resistance bands, free weights and jump ropes.
You can also do a dance unit, with line dancing and ballroom danicing.

These are great ideas to do with a smaller class size. To add on to your suggestion if you have the technology you could use WII just dance for kids as well.

It would be helpful to know the grade level of the students and ability level. With just 5 students there would be a lot of time for individual instruction in varying skills. You could also do cup stacking with the students if you are familiar with that. Rather than game type activities your lessons would be based more in skill development.

I like the suggestion of team teaching if that is an option, especially if it is a class with special needs. It is amazing to watch students work with others. It is a good time to work on lifelong skills otherwise.