This is a glitch that lets you pick up objects even though you are in a vehicle. The right trigger (RT) isn’t normally used to pick up objects while in a vehicle, it is instead used to drive forward or fly upward.
Here’s how you do it:
Stand in front of the item you want to pick up and have it selected as indicated by the yellow outline. Then, pause the game and change your vehicle. Right before the screen turns white and the vehicle is changed, there is a brief period where the item is selected. Press and hold RT during that time and you will will pick up the item. Now you should have it still picked up when you are in the vehicle.
Note that once you are in a vehicle, be careful to not drive or fly away too fast, since this will drop the item. Also note that you don’t have to keep holding down RT to lift the item while you are in the vehicle. Once you are holding it, you can’t release it. (Unless the item is too far away.)
The last thing I show in this video is that you can not have multiple vehicles using this glitch.