I feel incredibly old and mature saying this, but I'd go back in only for the important file box. All the material stuff can be replaced by insurance. If certain things were to be lost however it would make things such as being able to do my job difficult, so the box with all my insurance documents, passport, driving licence, bank documents etc would be the most important thing to grab.
This is assuming my phone/car keys/wallet are all in my pocket, which they should be. If not I'd have to grab those aswell. I personally don't have anything of sentimental value, we don't have photos or similar things