You can buy texture rubbing plates, but my favorite alternative is using plastic embroidery mesh panels that are made for cross stitching. If you buy them large and cut them up, they are pretty cheap. Give students white cards that measure 2.5" x 3.5". Challenge is to think of things that come with a grid-like texture. I’m happy to say that my students came up with a lot more options than I did, so who’s to say that kids today are less creative?