Well actually Arduino boards (and clones of course) can support a ton of real sensors, (light, noise, temperature etc.) and the internet and youtube host a ton of tutorials on how to mount them. I think you can do it vod! For the display i was thinking about something like a single hand held data pad with your oled display, wired with a small corrugated tube, in which you can run all the wires connected to your board, which will be on your backpack with all the sensors. And some flashing LEDs. LEDs make everything better. You know, something like:
If temperature >30°c then turn on Red led
If temperature <10°c then turn on blue led.