How did my son get to your house? Seriously, we tried the sticker system when he was in kindergarten last year and it completely back fired. He cried every time he didn't get a sticker, it was hard. We tried medication which helped a lot, but in the end decided the side effects were not worth it.
What worked for my son was diet changes; he's on milk (casein) free, gluten limited, additive, dye free diet. He takes fish oil, good quality daily vitamin, and a magnesium supplement.
He sees a counselor twice a month and Dh and I meet with her too. She gives all of us coping strategies and helps give DH and I realistic expectations for DS's behavior. For example it's realistic for us to expect him to be quiet and stay in his seat through a movie, it is not realistic for us to expect him to be perfectly still. We also need to provide him with tools to help him (a squeeze ball, gum to chew, and lots of exercise before we go).
I do make sure I have his attention when I talk to him. I touch his shoulder and crouch down so he is looking at me. He has to repeat back what I say.
We try to keep things simple, coat, shoes, back pack go in the same place every day. I try to vary our routine (we home school) so he doesn't get bored. But, re-reading your post it sounds like you have that covered with predictable routines.
Have you tried a written schedule of thing that need to be done? We do this with cleaning his room and school work. He checks each item off and if he loses track, he can refer back to the list. It removes me from the argument, I remind him to look at the list. It took a while, but he'll ask me to write a list for what he needs to do for other activities. He's gained self confidence and that has helped with his self control.
He takes a martial arts class three days a week, which has been very helpful.
We use the same language(self control, respect, responsibility) at home they use in class. My husband takes classes with him and it has helped them bond. It is something just between them, it has helped immensely as DH isn't very patient .
The other thing I do is wait. I'll say, "When you are ready to listen," and just wait until he focuses on me. I have to repeat myself several times on occasion, but after several weeks, he has gotten much better. He will stop moving and look right at me on the 1st or 2nd request. Then I ask "Are you ready?" and I go over whatever I need him to do. He repeats it back to me.
It seems to be working fairly well.
All these things together have made life more livable. I'm rarely angry or frustrated any more. I still yell once or twice a week, but he usually reminds me to use self control. My son is a lot less frustrated and feels much better about himself.