An upright bass is an unusual instrument in some types of music, such as an Irish tune session, as well as being a big instrument in what might be a crowded bar, so it'd be advisable to get a feel of the place before you heave it in.

So "whistle in the pocket, bass in the car", to start with, sounds like a good idea. If there is someone leading the session, no harm to have a chat first, but it's not always clear who that is.

If you go all set to enjoy the music, even if you don't play, but ready to play, if you feel up for it, that's the way to ensure a good evening. Sessions vary so much there aren't any rules you can predict. And Georgia is a long way from here, and I'm sure they do things differently.