Definitely, you can track a lot of dirt and salt in the house in winter. People should remove their shoes or make sure they are wiped good before dragging things like that into the house--and, if they don't like the way it's salted because of freezing rain, why didn't they cancel the whole boasting session for bad road conditions?
And those snacks--that is a privilege, not a right. And, making a big mess in someone else's house is a sure way to get that privilege revoked. People, especially small children, often do make pigs out of themselves. Small children are naturally messy as they don't yet have the ability to be neat. But, if the place is left trashed and the people responsible do not clean it up, they should stop those refreshments.
Worse, when people (and not always children) go wandering through the whole house without permission from the owner. Usually, the path leading to and from the study area (and the study area itself) is where people should be. If they are not specifically invited elsewhere, they should stay within those areas. Usually, this includes the bathroom--but, if people go and waste toilet paper or make and leave a mess (and that can just as easily be a soap mess in the sink as the other kind of mess), that shows they do not appreciate the householder. Not to mention things that turn up missing, or that end up getting busted, because someone was where they were not supposed to be.
Good thing I never had a book study group. Between dirt tracked in, people wandering around (and as often as not, snooping) everywhere throughout the house, things getting busted up, the occasional boy that pees in his pants (or worse, right on the floor), people making food messes, and not being able to get them out when they are supposed to, it is not worth it. Not to mention, if I have one small problem (such as something that resembles a "pagan" symbol, a "bad" record, or nice things that could be taken for materialism rather than I am sick of replacing crap all the time), the hounders would be down my throat about it.