At my last Halloween party, I served cat diarrhea with bones.
For the cat diarrhea, simply serve your favourite chili (homemade or store bought). I also used a cat shaped cookie cutter to cut out slices of cheese for my chili.
As you can see in the top right hand corner of the picture, I served this with bones bread sticks. I used store bought dough and shaped it into bones by tying the ends into knots before baking.