Literally, the term "scoop up" means "to use a scoop (like a small, deep shovel) to collect something that is difficult to collect by hand, such as a pile of dirt, or small rocks, or anything granular.
You can also scoop up something with your hands, in an action like using a scoop:
The child flung her arms around him as he knelt to scoop her up.
Figuratively, though, the term means to acquire something of value as a kind of bonus to some other action, and before someone else gets it or takes it away.
When playing Monopoly she always aimed to get Broadway and Park Place, but she would not hesitate to scoop up the utilities if given the opportunity.
Carrying the money from the vault, the thief paused to scoop up a small collection of rare coins he noticed. "Waste not, want not," he thought -- but his greed proved his undoing, as the coins were later the key evidence used to convict him of the crime.
In your example it's not clear whether the subject picked up the ice cream box in a scooping motion, or whether the box was a kind of added bonus, incidental to whatever else she was doing. We can assume the use is valid for the context, though.