Always wanted to share that special tiara with your teammate? The Rocket League devs have heard your prays and are coming with a special player-trade system!
First what you have to do is invite that person to your party. Otherwise the trading will not work. Another thing to remember is that common and Premium DLC items (DLC that you bought) can not be traded in with another person. The Premium DLC is special and thereby not exchangeable.
As for the XBOX players this feature will not function. Rocket League has asked Microsoft about this but it seems that the function is on hold for now. Will keep you updated about further info!