If you are using a remote control:
Just buy several different frequency crystals for your remote control. There will be a number on them, and just make sure it doesn't match with that of your opponent.
Any well run competition confiscates remotes from all participants who aren't competing to avoid interference.If you are using a microcontroller:
2.4GHz is just a frequency. Today, electronics uses fancy algorithms that go way beyond a single frequency.
For example, Bluetooth does what is called 'frequency hopping'. It actively looks for noisy channels and then avoids them, often transmitting data on 2 or 3 frequencies at the same time. I've found Bluetooth to be *extremely* resistant to interference.
But it's not something you can just throw together in a few days with resistors and capacitors. You have to buy a module for it.
Don't however use Xbee. They are very susceptible to interference.
I also sell a microcontroller with built-in Zigbee wireless:http://www.societyofrobots.com/axon_mote/
It uses the same Zigbee technology as the Xbee, however you can program it to do frequency hopping and noise analysis like Bluetooth. It won't be as resilient as Bluetooth, though. So why use it? Well, unlike Bluetooth, you can link up as many as you want to form a mesh network.
But since you only have 5 days left until your 18th deadline, I recommend finding a Bluetooth transceiver.