I use a Kata 3n1-10 as a sling bag (can convert as left or right sling bag with side opening on both sides or as a normal rucksack). Mine is the smallest model and there are 2 more in the same style. If it looks a bit like rain i use the waterproof cover. In regards to protection in event of a crash....i pay about 70 quid for 2800 quid worth of insurance on my camera gear or you could maybe add to home policy? A good back protector is something you should have to protect your back anyway.
Digital cameras i just shove anywhere as it is the slr gear i worry about due to all those moving parts as you said.
http://www.kata-bags.com/product.asp...&Version=Photo