Medical supplies/clothing and ammunition should have been a priority being Paulus was told to stay, Fuel would hog valuable cargo space.
All this takes time on limited rail lines from their origin to the Front.And there were 2 other Army Groups to supply.

The planes nor the ground crews were not prepared for the frigid weather.
The Russians bombing at night making even more work for exhausted/starving ground crews.

Maybe Hitler was hoping this airlift would work as the successful Demyansk[sp?]airlift was earlier.

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