Drinks at a hotel bar.
good topic.
Bitters, bar mixes, cocktail onions, olives, etc require proper hashgacha. Lemons are sometimes cut in the kitchen and even when cut at the bar, sometimes the knives are brought from the kitchen.
Alcohol is generally considered a davar charif so there's a potential issue for bar spoons, shakers, cobblers, etc. It would have to sit for at least 6 minutes for it to be na issue which is not the case for most mixing though they don't always rinse between mixes (though they're supposed to) which means there's a kavush concern on the residual.
We've also come across bar items such as copper mugs used for Moscow Mules, used for a soup bar which would be very problematic if the cocktails are charif then it would be prohibited to use them even aino be yomo.
As far as the alcohol itself, 'nuff has been spoken / written about that already.