Nope. I predict zero effect on the market.
Why?
Well, we'd have to have a shutdown in the first place. My guess is we'll see a continuing resolution which kicks the can down the road a month or six weeks. So I doubt we're even going to have a shutdown this weekend.
Secondly, we've had them before. They're getting to be old hat. I don't ever recall any shutdown being blamed for any market downturn.
Third, government spending is only about 20% of all economic activity. The private sector is the vast majority of spending.
Fourth, even when the government shuts down, only parts of it shut down. The military, Social Security, and the IRS will all be at work. I believe they close the National Parks, which is an inconvenience if you were planning to go there. But IIRC it is about 70% of the government remains open during a so-called shut down.
Could the market coincidentally drop any time now and will the media blame the shutdown? Possibly, if they don't blame North Korea or swear words or increasing energy or the spectre of inflation or the fact that it is Wednesday tomorrow. It is required that the media identify some cause when the market drops, even if that is not the real reason.
Because the market could drop, I have my asset allocation set the way I want it and I am rebalancing to that on a regular basis. That's all I do.