Yesterday FI and I attended the baptism of FI's niece. Afterwards there was a reception at a restaurant. We arrived and there were 2 bottles of wine on each table, one red, one white. In the room we were in there was also a bar which I went up to get some water. My FSIL (not the one who had her baby baptized) was behind me and ordered a beer for her H and a mixed drink for herself. A few seconds later she walked over to our table to see if any of us had cash because it was not an open bar. Luckily FI had money on him, but it was pretty awkward for FSIL to have to leave the bar to get money to pay for the drinks and would have been even worse if no one had cash on them. Then to top it off the beer was warm and the mixed drink had way to much alcohol in it.
So yeah. If you are having any event where only certain things are hosted (wine, water, soda, juice, etc) make sure there are signs up with what is hosted. Our table was right by the bar and we watched quite a few people have to give their drink back because they didn't know it wasn't free and had no cash on them.