Under the "[ContainerUIActive]" heading is likely where you need to re-assign the R key to what you want, as it is currently assigned to something called "ReRollContainer".
DefUser.ini makes mention of it under its "[ContainerUIActive]" heading with this comment:
Code:
;NOTE: Reload disabled in this context in favor of ReRollContainer
So what I've done is under that heading, the key that I've rebound to Reload (Shift) under default, I've bound to ReRollContainer under the [ContainerUIActive] heading.*
But again, I don't feel like wasting time swimming away from the plane crash a 5th time, going down the elevator thing, etc. just to see if it works. As far as I know there's no developer console to re-execute changes to the User.ini file, so any time I make a change, that's what we are talking about to get back to testing.
Luckily, later today I'll have the full game installed which allows saving. This means I'll be able to get to a part in the game that I can test out container use and tweak the controls to my liking... even if it means I have to edit ini files by hand. Which I'd rather not do.
*My guess is that at one point there was a function to flip through the contents of containers with this ReRollContainer command which is now defunct as as far as I can tell, there can only ever be 3 things in a container of any kind, and when you hit the Use button you grab everything no matter what. I'd love someone to correct this if needed.