I would feel extremely nervous travelling for 1-3 hours to get to an event that was outside of my comfort zone, particularly an "outing/drinking event" which would probably be very noisy and have a lot of rowdy people.
My advice would be to just try and enjoy yourself as much as possible so you forget about your anxieties, but obviously that can be very hard. Think to past occasions when you have had to be outside of your comfort zone, but that went well. Those show that you can cope!
As for the autism conference, people won't be surprised to see a person with a bit of social anxiety there. Everyone will be understanding, and the situation shouldn't be too stressful. If you have to give a talk, then if necessary you could try pretending you are speaking to an empty room, look down at your notes (with your eyes, not your head), or just try and relax.