Another thought, as obvious as it may seem, is to suggest simply trying to not be alone as much as possible. "There's safety in numbers" as they say. Maybe try to arrange to be in a (known friendly) crowd as much as possible.
>I'd suggest looking into a lightweight bullet-proof vest as well.
If you are worried about a sniper attack, lightweight bullet proof vests aren't going to help you. They don't stop high-powered rifle rounds. The only thing that stops high-powered rifle rounds would be the kind of body-armor the military uses, with ceramic plates. I don't think OP wants to spend the rest of his life wearing a 35lb vest. Fortunately, lightweight vests will stop small caliber handguns.
If you want to get really paranoid, you can imagine a vector where somebody attacks by, say, intercepting your pizza delivery and adding poison to it or something. :-(
I don't know how you feel about guns, or even if you're eligible to own a gun in the US (not sure how citizenship status affects that). But if possible, you might considering purchasing a pistol and look into getting a concealed carry permit (if required in your state). If you do, get some training and take training seriously.
Short of a gun, spending some time studying a martial art could be beneficial. Brazilian Jiu-jitsu and/or Krav Maga might be good choices. Escrima could also be good... they put a lot of emphasis on "stick fighting" and you can certainly legally own a stick... and that may be more acceptable if you oppose guns on some kind of philosophical basis.