james my ds is also nearly 8yo and has ASD (HF). We've got the same issues about screen time here too (with the nintendo ds). Not quite as easy as "just take it away and let them do gardening/cooking instead" or "he'll find something else to do" ha ha ha ffs
The point is that anything has the potential to become obsessive, and screen-based things are much more likely to be so, in the same way that electronic toddler toys (i.e. lights/sounds) are to toddlers with asd . Also as anyone would know who has experience of autism, normal play activities are severely limited/stereotypical, and in most cases almost entirely absent - it's a defining characteristic. Even if the screen-time activity was replaced by something deemed healthy e.g. cooking, it's the obsessiveness that is the problem.
Anyway, back to the OP. This term ds has had less clubs than normal after school and I am noticing a massive difference. He'll also throw himself around saying he's bored etc. My plan is to get back on track with as many after school/weekend activities as possible, especially sport. Also thinking for the first time about getting a trampoline (argh, hate them!) as the sofa-bouncing is getting excessive now.
Wrt to alternative activities. Million dollar question! Does he like magazines/activity books? Ds loves Doctor Who and some of the Marvel stuff, so we get a lot of those. Recently Tintin activities which are great. Also lots of non-fiction reading, so encyclopaedias, compendiums, atlases etc. The downside is that I'm followed round the house with "mummy, did you know that…." aaaall the time 
But my sympathies - we did ABA relatively intensively for four years and never fully cracked the play thing!
We also do have clear rules about screen time, which he knows and is reminded of even if he asks (e.g. he knows that he doesn't ever have it before school, or before supper on weekdays). Does your ds accept rules?
Does he have siblings? I have a younger dd (NT) who is 5yo, and they are playing together more now, which helps.
Look at the SN boards - I haven't been on much recently but there are usually lots of threads about helping with play/activities.