There might be a fair bit of having to "tag along" to things after hours if you are not in charge. You might feel you can't beg off social things. It is fair enough that you go and join everyone for dinner. However, once the main social obligation is over (e.g. dinner) you should not feel you have to "kick on" (a thing that I frequently used to do and it rarely ended well). You should not have to go onto a bar or club or whatever. If I were you, I'd just quietly say good night at the end of dinner and go back to your accommodation. If they are a big drinking group, there will be hangovers nursed the next day, breakfast skipped, even possibly people coming in late for morning meetings etc., but your absence from the big evening out will NOT be missed. You'll be sharp and on top of your game (and so, before you know it you will no longer be "bottom of the food chain"
).