Boxing up, which means to pack or organize things into boxes, can have several antonyms depending on the context. If we are talking about the opposite of packing, then the antonym would be unpacking or removing items from boxes. On the other hand, if we are looking for an antonym for organizing, then the opposite would be disorganizing or scattering items around. Another antonym could be donating, which means to give away items that one no longer needs or wants. Lastly, if we are talking about shipping, dispatching or sending items out, then the antonym would be receiving or getting things in. Therefore, the antonym of boxing up can vary depending on the specific action being referred to.