When you buy an RTR model, there are some extras that will probably need to be purchased. You will need batteries for the transmitter and maybe some for the receiver depending on the model. You will also need to buy some fuel as well as a squeeze bottle to dispense it into the vehicle. Depending on the brand of truck you will need to get a battery and charger for the starting wand or roto-start.
It's probably a good idea to get a couple of extra glow pugs as well.