Originally Posted by Wayne's Striple
You don't want a helmet flopping around on the back of your bike; just give it to your gf and she has it when you pick her up.
and when they break up he's out the cost of a helmet.
the single best option has been posted and reposted. the elastic nets are the way to go. you can hook to just about anything under the tail, even wrap it around and hook it to itself if you want to. not to mention that they aren't cost prohibitive, and you can throw em under the seat while riding anyway.