You might run into some smaller, independent stores that are closed on Friday afternoon, but it really depends on what US town/city you'll be in, but most of the chain-type stores should be open.
A lot of stores will be closed on Sunday, but there will still be some stores open, depending on what they are.
The only coupon for Michael's I saw was the normal 40% off one item that's almost always in their ad.
Have fun shopping