I think the biggest impact would come from everyone choosing acceptable alternatives to everyday items. I made the point in a boycott thread that the high street didn't die because everyone stopped buying anything at all from high street shops but simply because fewer people shopped there and on average they bought less.
So DS1's chocolate fairy is buying own brand or British brands instead of mars or Cadburys. It all goes down the same way. I can go back to Finish instead of Fairy in the dishwasher. Simple swaps.
Smaller businesses are tougher. So many good independent sewing pattern companies are American. Many more are Canadian, Australian, European or British, though so all things being equal I would probably favour those for similar patterns. And that quilting that I do a bit of - it's largely American in its origins, even if other parts of the world have similar so many of the fabric brands and designers are also American.
My curly hair products are almost all American. Some are black owned businesses and I have no qualms about continuing to support them as long as they are available here. My conditioner is owned by Unilever, now. I spent a fortune before I landed on it and I'm actually not allergic to it so that's more difficult.
And, much as I hate the corporation.you can snatch my caffeine free diet coke from my cold, dead hands. It gets mixed with Vodka - European, of course and sometimes so local that it's hand delivered to my door. I did try the Tesco version and was still tasting it a day later 🤢