You need the small crystal for the yellow radio and the yellow cord to plug it into the cortex.
You need the big (L shape) crystal for the back of the RC radio.
You need a serial/usb to RJ connecter programming cable.
The crystals is how you pick what channel to run on. There is 30 pairs, 10 pairs were public channels, 20 pairs were used only for competitions, that is how they kept robots from interfering with each other.
The VEX RF channels are crystal controlled. The basic kit comes with channel 61, the add on transmitter/reciever uses channel 89. There are two kits of 4 channels each that can be purchased. The transmitter is FM modulated
Channel 61, 75.410 Mhz - Starter kit
Channel 63, 75.450 Mhz - Upgrade kit B
Channel 65, 75.490 Mhz - Upgrade kit A
Channel 67, 75.530 Mhz - Upgrade kit B
Channel 69, 75.570 Mhz - Upgrade kit A
Channel 81, 75.810 Mhz - Upgrade kit A
Channel 83, 75.850 Mhz - Upgrade kit B
Channel 85, 75.890 Mhz - Upgrade kit A
Channel 87, 75.930 Mhz - Upgrade kit B
Channel 89, 75.970 MHz - Additional receiver kit
The competition kit is not sold, it is only for events.
Channel 62, 75.430 Mhz - Competition kit
Channel 64, 75.470 Mhz - Competition kit
Channel 66, 75.510 Mhz - Competition kit
Channel 68, 75.550 Mhz - Competition kit
Channel 70, 75.590 Mhz - Competition kit
Channel 71, 75.610 Mhz - Competition kit
Channel 72, 75.630 Mhz - Competition kit
Channel 73, 75.650 Mhz - Competition kit
Channel 74, 75.670 Mhz - Competition kit
Channel 75, 75.690 Mhz - Competition kit
Channel 76, 75.710 Mhz - Competition kit
Channel 77, 75.730 Mhz - Competition kit
Channel 78, 75.750 Mhz - Competition kit
Channel 79, 75.770 Mhz - Competition kit
Channel 80, 75.790 Mhz - Competition kit
Channel 82, 75.830 Mhz - Competition kit
Channel 84, 75.870 Mhz - Competition kit
Channel 86, 75.910 Mhz - Competition kit
Channel 88, 75.950 Mhz - Competition kit
Channel 90, 75.990 Mhz - Competition kit