For me - two options.
1) a pair of kevlar draggin jeans, bike boots and bike jacket. When you are ready to walk - boots/jacket and helmet into GS boxes.
2) Same as (1) but wear rohan or craghopper walking trews under textile armoured trousers and just take the bike gear off when you are ready to walk, stick on walk boots and walk jacket and leave rest of gear with bike.
I would agree with the comments above, yes don't ride like a loon, and you prob won't die in an accident, but sliding down the road in normal jeans or walking trousers I would guess is not recommended. I would add from a friends experience, walking boots are not ideal ankle protection on a bike - wear proper bike boots. Ankles take quite a long time to heal and are complex joints so having them in a decent bike boot is a must for me.