I've seen some drivers allow some people with food/drinks on the bus and then block others. It has always appeared to be a bit of a common sense discression thing . . . drivers that will allow adults with bottled water or babies with a baggie of Cheerios on but stop the five year old with the Mickey ice cream bar or people with coffee and no lid. I think if it will be easily cleaned up or have a very low probablility of making a mess they allow it, pretty much, though they in no way have to. Technically it is not allowed.