You Don't Holler "Unattended Bag".

As the government won't, we should train ourselves to survive an Improvised Explosive Devise.  (IED).
Citizens of Israel are so well 'trained' that an unattended bag or package would be reported in seconds by citizen(s) who know to publicly shout, 'Unattended Bag!' The area would be quickly and calmly cleared by the citizens themselves.
If the spectators who saw the (explosive) backpacks unattended at the Boston Marathon had shouted the warning and the other people close by knew what that meant many would have quickly left the area and the injured would have been far less. 

They announce a similar warning at airports not to leave your bag(s) unattended or to report any unattended bags; why not be aware of unattended bags  in the streets?  Especially at crowded events.

In a recent test five bags were left unattended in strategic busy locations.  Everyone just looked and walked past.  Except one person, he tried to steal it - BOOM!!!!!
But if you weren't injured in the Boston explosions it's much easier just to remain stupid.

Additional survival method if you don't have time to get away.    (Copy and paste into browser).