I totally agree with
Nordic Cat and Mike above, the sky is the limit with what you can put on a cat. Space for toys is never normally an issue on a cat but be careful as weight is. The more you add the more it will affect performance.
In addition to Mike's list above you can also have icemakers, washer/dryers,
cockpit wet bars, dive compressors and I've even seen a bath tub on a St Francis 50!
Regards
Adaero