Springtime in the rockies can be interesting - hot and sunny, the cold and windy, then some rain or snow followed by hail and maybe sun again.

My bike (caad9 with no attachments for racks) is not equipped in any way to carry extra clothes for changing weather. Obviously I could use a backpack but I'd rather strap stuff to the bike if possible. I was thinking of a bungee around a jacket and my top tube but there are cables passing under and could bind. Saddle bag isn't big enough for my jacket or a pair of pants much less both plus tubes, etc.

Anyone have an ingenious method for carrying stuff on a bike without racks or packs?