Question: Is it correct that one may not sit on top of a box containing food or beverages?
Answer: The Gemara in Masechet Berachot (50b) states that it is forbidden to act in a degrading manner towards food. Thus, one may not, for instance, use a piece of cake to wipe up a drink that spilled on the floor, for this is degrading towards the cake; this is especially true since this will cause the cake to be ruined and no longer be edible.
The Reason for the Prohibition Against Acting Disparagingly Towards Food
The reason why it is prohibited to act in a degrading manner towards food is because food is an integral component of the abundance which Hashem showers upon us. If one treats it disrespectfully, he is in essence stomping on the goodness which Hashem bestowed upon him. There are additional reasons for this as well.
All of the laws regarding the prohibition of acting degradingly towards food are discussed explicitly in the Gemara Masechet Berachot and Shulchan Aruch (Orach Chaim, Chapter 171).
Sitting on Foods and Beverages
Regarding the above question about whether or not it is forbidden to sit on top of boxes of food and drink, the Tur and Maran Ha’Shulchan Aruch (ibid, Section 2) rule based on the Baraita in Masechet Sofrim, as follows: “One may not sit on top of a box containing figs and dates; however, one may sit on top of a cake of pressed figs or a box filled with legumes.”
This means that one may not sit on top of food items which can become ruined by sitting on them, such as a sack filled with figs, for figs are easily crushed and smashed. It is therefore forbidden to sit on them, for doing so causes them to be ruined. One who does so transgresses the prohibition of acting disrespectfully towards food.
However, it is permissible to sit on a solid box filled with figs since doing so will cause no damage to the figs. It is likewise permissible to sit on a sack filled with dried legumes (beans and the like), for doing so will not cause it to be ruined.
Based on this, it would seem that it should be permissible to sit on a case filled with beverages since doing so does not cause them any damage. However, sitting on top of foods which may become ruined by doing so, such as cakes or cookies, is strictly forbidden.