Q: I am having a cash bar at our wedding. How do I put this on the invitations? Do I just put "Cash Bar" at the end?
A: I can understand the dilemma because you'll want people to come prepared but there's little etiquette information available that tells you how to get the message across. I think you're on the right track here...yes, there should be some mention of the cash bar on the invitation itself. Usually, it's nice to have that information embedded within a complete sentence, so as to send the message through in a subtle way. For example:
"Please join us for an all-inclusive dinner and a cash bar. Reception to be held at..."
"We would like to treat our loved ones to dinner at... Cash bar available."
These are just a few ideas. You're welcome to use them word for word, or to manipulate the wording to best suit your needs. At the very least, I hope they sparked some ideas for you on how to word the invitations. I would certainly say that this is the only way to get the message across. If by chance, you are designing a wedding website, it would be great to post the cash bar information on there as well.