After 16 years of teaching and trying many strategies to find a way to have students bring their materials to class I have finally found a method that works for me and my 8th grade students!
It is called the "oops" record. I explain to students that "oops" happens everyone once in awhile. Oops I forgot my book, oops I grabbed the wrong folder, etc (you know them, you have heard them all). I have students sign my oops record and get the required material if necessary. I explain though, that after two oops, it isn't an oops anymore, rather, it is 'I am failing to be prepared for class.' The third time a detention is issued. Believe it or not I very rarely have to assign a detention! There has been the occasional student who receives a detention (and sometimes more than one). That is when I call home, but again it rarely happens. Most students find this system to be very reasonable. That is what it is all about, having your students buy into your strategy.