starter kit question... looking for suggestions for 9v toy/gadget to cannabilize

hello - new to arduino and looking forward to the tinkering/learning. in the starter kit i purchased, it lists 'things you need to supply' which includes a 9v device that includes a switch/pushbutton that i'll be hacking. i'm having trouble thinking of anything... the only thing i have lying around are those little flashlight caps that you snap on to a 9v battery. they have a switch, but i don't know if that would be good enough? i don't know if i need to prefer something that has a case that can be opened (i.e., screws, or snapped together).

adv-thanks-ance

robin badart tucson, az

To provide some context to the forum members who don't own the book, the project is "Project 15: Hacking Buttons". Here is the project's sketch: https://github.com/arduino/arduino-examples/blob/1.9.0/examples/10.StarterKit_BasicKit/p15_HackingButtons/p15_HackingButtons.ino

Forum thread providing links to PDFs of likely outdated, but still serviceable, versions of the Creative Commons licensed Arduino Projects book: https://forum.arduino.cc/index.php?topic=666271