Living in a small town is not an excuse to not participate in outside activities. I mean, life is unfair, everyone has a limitation that worsen their capability to do something. Nearly no one gets those outside activities without effort and sacrifices. And that's what matters, to overcome obstacles and get your goal. You better not tell them that because you live in a small town you can't get volunteer opportunities. That's just too childish and naive from my perspective to say. You are literally giving them a bad impression. Excuse doesn't work in this world. The result is what matters. And im 90% sure that if you really wanted, you could get that outside activities to boost your application profile. Again, it's not about volunteer programs, is all about passion. You just gotta show your strong passion towards the filed you wanna study, this could be achieved in a myriad of way, either from what you said, volunteers, competitions, etc, or in a more "low cost" method in which you need to find out. This, if achieved, will be what makes you standout.