Using a barrel is a pain! Only the top left (1st item) and bottom left item/s are selectable. You cannot freely select an item in the barrel. This is not limited to barrels as it has happened with general inventory items too like backpacks.
This means that in the majority of cases you have to take everything out on the floor just to get one thing and put it back again.
Also the menu clipping so you can't even see the full list of items.