apushatayid,
It seems that the main gezeira was indeed to prevent drinking with them but it was enacted in a situation which could come to that; that’s why it’s okay to bring it back to your house, but not to drink it there.
As far as Coke, the poskim argue about whether a non-alcoholic beverage is included (and as pointed out by ravshalom, the R”ma even allows most alcoholic beverages). I think that the only non-alcoholic beverages which might be included are those used socially, such as coffee, but not water or even Coke.