I think it's hard to say whether it will directly impact most people who don't work for the government (but that is a lot of people, upwards of 2 million). "Essential" functions remain, which means that military, border patrol, food inspectors, mailmen, air traffic controllers, etc, will all still be working, although they don't get a paycheck during the shutdown. Non-essential staff will be furloughed without pay, which only directly affects you if, say, you were planning on visiting a national park, getting a passport processed, or applying for a small business loan, for example (at the lab in which I work, we are planning to submit several grant application to the NIH; I'm sure that will be on hold). Most people won't do those things for the short time the government will be offline. But I think that (a) because hundreds of thousands of people will be suddenly out of work, and (b) there will be a general sense of panic, that this will impact the economy negatively. In that sense, it may have an indirect impact on all of us.