One drill that I like (that I didn't see), is doing a standing roundoff up and off a wedge. The hands go at the top of the wedge and the feet land on the floor. It forces the gymnast to give a good push off that bottom leg and drive the back leg over. Because their hands are already waist high, they tend to pull them up more easily. I haven't seen a gymnast pike this drill down. We also do RO from one knee for some of the same reasons, but they usually pike it down.
Also, someone said that they aren't sure about doing the RO over a cheese or barrel. We do them over small cheese mats on their side. It is very safe and forces the gymnast to stand up rather than pull feet down. Also, it forces the arms to be up when landing or the mat will get knocked over. Kids are a little nervous about it at first, but the first time they fall on the cheese mat, they find out that they don't get hurt. The problem with an octogon is that it rolls and could push the gymnast back on his head.
I don't like the cartwheel landing with the arms down. It doesn't make sense to me -- especially not for a connection. Arms go by the ears except when they are snapping back for the BHS. As someone pointed out, we don't connect skills with an arm swing.