In regards to the question "What solutions of you have to increase impulse purchases at self-checkout?" I'm seeing retailers lean towards suggested items based on what the consumer has scanned. Let's say the consumer is at a Banana Republic purchasing a pair of women's dark wash skinny jeans — some suggested items would be a stripped tank, a jacket, some flats or sandals, etc. A message would pop-up such as "this shirt goes great with the ABC dark wash jeans" with an "add to cart" option, in which they are prompted to pick out the size and color of the item they want to add. A store associate would then get a notification to bring the item up to the customer at self-checkout station. Granted, this slows down the process, which is the one of the main purposes of self-checkout, but can increase impulse buys.
Another solution being the size of the POS hardware. It takes up too much space to have a rack full of small impulse items you'd find at the regular checkout line. Get an iPad POS system!