http://www.sportsbikeshop.co.uk/motorcycle_parts/content_prod/231761
Tempted by one of these myself tbh.
Silly question but is there an easy way to chain a motorcycle up to a car?

There's nothing especially dangerous about a 10kg chain secured in a pillion carrier. Make sure the strap side is on top and adjust the strap ends so it clips down tight.Yeah, guess you are right, a 10kg chain can be something dangerous.I will need to find a safer way to carry it, when I get my hands on it will be easier to think on something else.
I was checking this ones: http://www.autokicker.com/products/motorcycle-luggage/tail-bags.html
looks like to be good quality.

I will get an Almax 16mm or 19mm... not sure yet... but needs to be 2 or 2.5M, I need to measure the pillar I will attach to
Not sure about the padlock yet, but I need to decide it asap because I will collect my bike next Tuesday.
I just got the chain/padlock package cause I genuinely have no idea how you choose the right padlock. I mean how do you know it'll fit the chain and how do you know the padlock isn't crap, cause I assume on a 16mm+ chain the padlock will be the weakest link.
For general luggage, quite possibly...I was checking this ones: http://www.autokicker.com/products/motorcycle-luggage/tail-bags.html
looks like to be good quality.
Avoid anything where the key looks like your normal front door one.I've seen a few good deals on chains only and used chains which I fancied buying but does anyone how you choose the right padlock?
For general luggage, quite possibly...
But as a lock carrier - No way. Too big and open. A proper chain carrier will be tight on the seat and just about big enough to get your sandwiches in.