For a horn, any little buzzer you can buy from somewhere like radioshack would work, something like a 5-12v item would work with this:
http://www.dimensionengineering.com/PicoSwitch.htm
Put a small ~9v battery on one side, and the buzzer on the other, then you can turn it on and off via the rx.
You wont be able to turn the truck on and off though- the rx needs power in order to control the switch, so if you switch the truck off some how via the esc = no power.
For lights, you could either use the picoswitch above + some large LEDS, or use the item below for a simpler setup:
http://www.dimensionengineering.com/EasyLights.htm