It doesn't make much sense that my character takes the in-game equivalent of several minutes to throw a bag into an empty car trunk.
The time required to store or retrieve an item should depend on how full the relevant containers are:
For example:
If a container is less than 1/3rd full, storing items would be instantaneous.
If a container is between 1/3rd and 2/3rds, it would take an increasing amount of time (between 0 and the current time).
If a container is more than 2/3rds full, it would take the same time it currently does.
Note: this should also take into account the container the item is being transferred from, not just into. So, if you're taking an item out of a full bag and putting it into an empty box, there would still be a delay to "retrieve" the item from the bag, even if putting it into the box is instantaneous.