I usually put detergent of some kind at the bottom of the cart. Also, I rarely only buy 3 or 4 other items. I HATE putting something on the bottom, but I've gotten it down to a science.
I always leave coupons in the cart. After I hear the total, I reach to get my coupons and "notice" the item under my cart as well. The MSC is happy because the item (if missed) is AFTER coupons, which clearly shows that it was missed. I just have to make sure that I have a coupon for something in my cart...which usually isn't a difficult thing for me to do