Please don't do a double degree for the sake of it. 9/10 times unless your doing law/economics or maths which is relevant it won't help you differentiate yourself very much at all. I'm speaking of course if your looking to do something in Accounting/Economics/Finance. For example Media might help if your looking to do marketing, and wish to close in on that specific industry. But really the degrees you mentioned (apart from Maths/Stats in the Science degree) won't pull you any better job prospects then someone with a single Bcomm.
They really do look for relevance if you mention your second degree,and if its not, then you can forget putting it on the table. People usually do a second degree(that's not relevant) because they use it as a back up for another job(that isn't commerce) or because they just enjoy it.
Really though you have to think if you want to spend another 2 years at Uni.Or you could already work for 2 years, make money and be potentially promoted and on higher foot then someone who did a double degree and is just starting on his grad job the same way you did 2 years ago with a single degree. You have to think if the job your aiming for really requires a second degree to signifcantly increase your prospects enough that spending another 2 years in uni and racking up more fees will be worth it.(jobs like IB,Consulting,or Law(where double is compulsory) make sense for someone to do a double degree, where as a job in Accounting or a commercial bank usually means a single Bcomm with good marks is a much more viable.) option).
Like Trans mentioned if your unsure of your career path yet then a double degree isn't bad, but if you know you want to do something in the commerce industry then try to do a relevant degree(which would be science majoring in maths/stats from your three), otherwise your job prospects aren't going to increase anymore then someone with a single Bcomm(unless you can really sell it hard somehow,but it's not easy).