I work at a Walmart Supercenter and tonight I was thinking what if it was attacked by 19 or 20 terrorists on a busy weekend.
Have the terrorists in the right spots at the right instant and most of the customers and staff would be caught before they would know what was going on.
Have a remote controled car bomb go off outside the local police station to buy some time as for the terrorists to empty the cash office and registors and maybe other high value stuff such as drugs from the pharmancy and send that loot out before the cops arrive while bringing in equipment needed for the hostage standoff like welders, homemade bombs, etc.
weld all the fire doors shut (most can't be open from the outside anyway but to keep hostages from escaping). Have control of the sporting goods weapons and ammo and the storage gun lockers in the backroom (even if the terrorists didn't bring in much weapons or ammo the store would have plenty for them to use.)
Move the hostages to the most secure areas, have some move store shelves and carts and such as to create baracades to hinder rescue forces. Have secure communications by technology or codes to your friends outside and force your hostages to give up debit card pin numbers and credit cards,etc so that your terrorists on the outside can raid the hostages bank accounts.
Have your connections overseas have Walmart stock shorted so that when the price falls when the news of the hostage they make a killing on the stock market.
Done right the terrorists make a pretty good profit, they have plenty of ammo and food in a supercenter to live on so they should drag things out. The longer such a hostage situation lasts the weaker it makes the President looks and if on the other hand a rescue attempt results in the death of many hostages that too reflects badly on the President.
Pretty much a Win/Win situation for the Terrorists that we need to be prepared to deal with.
You created a realistic and chilling picture. I've had similar thoughts, on different soft spots. None of which I'm willing to put on an open forum.
Tanks to break in, smoke and concussion grenades.