Don't be so timid people. The authorities are not going to be able to do the job alone.
If you see someone in an airline terminal set a piece of luggage down and start to walk away, tell them they can not leave that package there. If someone comes into your store and is buying quanities that are suspicious or a mixture of items that are suspicious, ask them what they want with those items. If the sqirm, are evasive or get mad, tell them to leave the store you are not selling it to them.