Regarding bungee nets and the like. I used a cheap bungee net once on my rack but it got stretched and soon became useless. I understand that the Delta net is very good and well reviewed.
I've been using the TECHKIN three hook bicycle cargo tie.
http://www.aliexpress.com/item/21423...604597329.html
They've held up extremely well for around 5 months of use and show little wear and no perceivable stretching. A couple of these and anything can be strapped on to a rack.
I combine this with a Roswheel 14224 6 litre seat post bag for my phone, wallet, tools and the like.
http://www.roswheel.com/en/prshow.asp?id=266