What are you going to do against a modern army? Poke Abrams tanks with a sharp 3D-printed stick? Perhaps, shoot bombers from your handgun? You can not win against a modern army using only light weapons. There's no question about it. Can you remind me which military has given something beyond token resistance to the US army lately?
Sure, if you want to use terrorist tactics (hiding between civilians, striking off-duty soldiers - that sort of thing) then you can make the life of an occupying army a living hell. But if you're thinking about using terrorist weapons with impunity, then have you ever thought about an army that doesn't have modern rules of engagement?
Oh, I get it. You'd prefer to kill toddlers, perhaps even primary school children. That'll surely help your cause.