What "props" can you use in an active older adult water exercise class that would make the participants have more fun?

Noodles are simple and cheap. Sometimes plastic balls (children's balls) can be used for resistance. When I taught water fitness my classes loved the webbed gloves for more intensity. If they put on belts you can do deep water aerobics even with those who do not swim well since the belts keep the students supported.
Back in the day (before all this amazing water tools) we used things like milk or OJ jugs (sealed), rubber 4-square balls and we even tried tubing and dynabands. They did not last long as the pools were chlorinated and the chlorine took it's toll!

Noodles are the favorite "toys" in my senior aqua classes; and they're cheap! I also use frizbees, paddles, fins (held with hands), small plastic balls from the Dollar Store, and junior-size kickboards. Members like "toys" but the personality/presence of the instructor is the most important ingredient for happy aqua exercisers.

I've discovered that the best tool you can give someone to use is their body. When people can use just their body and feel the water... they then can use the same moves when they travel. Many of my students actually do many of the class moves in pools when they travel.

Aqua paddles. They can adjust to the individual's abilities