When you install the Petduino code library, this comes bundled with a whole bunch of example projects, including a collection of baseline pet routines complete with simple animations and interactions. Whilst these are a great way to get an instant result, they really are just a starting point.
To extend your Petduino further, be sure to learn the basics of programming your Petduino and then checkout the other examples to see how to interact with the various components and start to make your own creations. Want your pet to shiver if it gets too cold? then checkout the temperature sensor demo. Want your pet to go to sleep if it starts to get dark? then checkout the LDR sensor demo. Or how about something completely different, like playing computer games? then be sure to checkout the game demos.
Every Petduino comes complete with a set of ear / arm accessories for you to choose what type of pet your Petduino is.
If you have access to a laser cutter though, why not experiment with creating your own accessories. All the accessories are made from standard 3mm acrylic sheets, with 3mm diameter holes with a minimum 7mm outer diameter, so just use this as a starting point and go create your own addons.
However you extend your Petduino, be sure to share it with us on social media by tagging your posts with the #petduino hashtag.