Perfect Relative Immobility:
You can become immovable in relation to a singular something you are in physical contact with at the time of activation. While active, you are unable to move your body in any way but maintaining the position is effortless for you.
While active, any external force applied to you is nullified. Your own weight is added to the weight of the object you are bound to and if the object is moved, you are moved with it.
If the object is somehow broken/destroyed at the points of contact which you have with it, this power is immediatelly disabled for 10 seconds.
E.g.: A car is about to run you over, you activate your ability relative to the ground and the car smashes into you as if you were an immovable bollard. After the impact and dust settles, you deacitvate the ability and leave unscathed.
Or you lift yourself to a flagpole position and activate relative to the pole. You now hold the position completely motionless for however long you want without effort before you deactivate it and get back down as if nothing happened.
Inventory:
The maximum amount of weight you are currently able to lift in a controlled manner even for a moment now becomes your inventory carry limit.
You are able to freely stash and retrieve any item that you own or are responsible for without feeling any weight added whatsoever. When the limit is reached your entire body becomes 100% immobile until you drop something out of your inventory.
You are still able to carry things manually and these items do not count towards the carry limit. They however behave as normal items weight-wise.
You may improve your carry limit by working out (The limit is always determined by how much you can lift.) and it will never decrease even if you grow old and won't be able to lift nearly as much.
Items are stashed and retrieved into your hand. When completely immobile, items will get placed on the ground directly under you or to the closest free space available.
You are always aware of your exact current value and capacity in a HUD indicator only you can see. You cannot stash anything that is alive such as humans or animals. Plants are ok.
Law enforcement and other security personel become aware and are able to check the contents of your inventory if they perform a search on you for whatever reason. They become aware of the inventory system the moment they request a search. (But it is not treated as an unbelievable superpower but rather as a closed bag.) At that point they are aware of the inventory, but not the contents yet. The contents are revealed upon search.