You WILL lose loose articles on FJ. Your ride vehicle is on the end of a robot arm, hence a LOT of motion. I don't want to tell any spoilers, so just take my word for it has someone who has ridden it way too many times.
Cargo pants with pockets that button or tie are your friend. I wear 'em to WWoHP whenever I go, and I look like a pack mule with all the pockets bulging.