Great idea. I might even suggest it where I work, thank you!
The company I work for allow for a three month handover with maternity cover person before and after mat leave - I felt it was a bit much and like I was being pushed out early and on return I just wanted my job back after a couple of weeks as I knew how to do it! Thankfully it was a flexible arrangement so I was back in role sooner than they planned and my cover moved on to another job.
Someone to go over IT changes would have been helpful. Also relevant staff changes.
I would have liked my boss to send an email to those who needed to know I was back instead of people not realising and still contacting my cover for a while. I ended up doing it myself but I felt a bit strange doing it, like I was trying to assert myself (bet no man would have worried about that 
)
Before I went on leave I was sent a clear spreadsheet of my mat leave pay calculated by week and monthly pay. Very helpful in planning!
Someone to tell me my options for using accrued holiday (including bank holidays which I think they'd have happily not mentioned I accrued if another working mum hadn't told me about) - either take in a block to extend leave or phased return. Seems obvious now but I didn't think the second option would be an option with my company to be honest.
Somewhere to pump on KIT days / on return if required. Not the toilets!
A bit of emotional intelligence / support / understanding from supervision about the fact I'd just left my child to return to work.
A review of the risk assessment that they were supposed to do in case I was still BF - that got neglected. (Maybe industry specific?)