Here are a few faves from around the Internet ... go-to sites that I use just about every week!
Need to spruce up your Google Slides? Check out this site for great free templates!
Need "creative commons zero" photos to upgrade your slides, your blog, various projects? Check out Pexels or Pixabay or StockSnap!
Need a video or two for the student who missed a key lesson? Check out PatrickJMT's free math videos!
MTBoS Search Engine ... search hundreds of math blogs for help!
And for the quick warm-up ideas ... oh my ... so many choices! But one I like for the challenge often presented is Median by Don Steward.