Making stuff is always really cool, perhaps you can add on a Piccolo and they can "create" a business card. Piccolo site: http://www.piccolo.cc/ 

or you could add on a LED panel they can program animations on in python, I hear even Neopixels are supported on the Pi now, Also, you could include different filters to add different affects to the LEDS. Adafruit has a 8x 8 matrix,  https://www.adafruit.com/products/2871

Perhaps even integrate the pi camera to "display"  a photo on the LED panel, or even live feed. I don't know. 

games are always good, minecraft and CeedUniverse are good games in that line.  https://www.pi-top.com/product/ceed-universe

Perhaps even a small 3d printer module. I know all this is money intensive, 

so a few non-money ideas, create a twitterbot that tweets when you press a button, or a light that blinks when a new hackaday post goes live, or a bieber post or whoever the cool kids are following these days

you could try to use those bluetooth sensors to create a webpage that displays the termpature in your room using this adafruit sensor, https://learn.adafruit.com/bluetooth-temperature-and-humidity-sensor/introduction

or a sit down sensor, use a force sensor to find out when your dad sits at his desk. but these require more hardware intensive immersion. 

auto on when you come in the room if a PIR sensor is hooked up, playa welcome video when you wlak in the room. 

Are there any Music programs on the PI you can use to remix or create techno music? 

can you add a microphone and make a basic remixing station? 

you have a computer with IO, think about all the things you can create to create more things!