Ah, this is an easy one. The answer here is an assault rifle with the necessary conversion to change it into a proper sniper rifle. It'll have all the necessary settings. Single for occasions where I can take aim, burst for times when 'best guess' is the better option, and full-auto for those situations where I need to slow down a group and RUN.
If we're assuming that I not only have the game experience but my actual knowledge, than I have a crowbar as well, and my retractible club where the crowbar doesn't apply. We can also assume that game resources means that I can actually find and conserve ammunition properly, so I will be able to do the things I said above.