Well, it makes common sense that you don't want to bring weapons (guns and knives in particular) on to a plane, you don't need someone telling you that, but let's take a look at things you might have trouble with bringing through security:

Cheese:  The TSA and security in European airports have confiscated my cheese (especially French and Italian cheeses) on more than one occasion. My suspicion is that it may resemble some type of explosive material.   I have learned that a safe way to bring cheese on a flight is to purchase it at a shop after going through security.

Soap:  Full bars of soap are also not appreciated by TSA and security scanners, probably for the same reasons cheese are not appreicated.

Toys:  If bringing toys through security, no matter how small, make sure they cannot be construed, in any shape or form, as a gun or weapon.  I once saw a tiny, tiny ornamental toy gun from a "Pirates of the Carribean" souvenir shop in Disney Paris be confiscated by airport security at Charles de Gaulle airport.

Booze:  They will let you take those small bottles of liquor (under 4 oz) on the plane.  But don't even try to consume them on board.  It is a serious violation and stiff penalties can be assessed if you are caught. 

Contraband:  Did you pick up some Cubans, cigars that is, while in Europe?   Those will be taken away by security.  I wonder where they wind up after being confiscated?

Grooming Aids:  Scissors will be snatched by security.  Sometimes they will take metal nail files and even clippers.  If you need to pack these items, make sure they are shorter than 4 fingers held together on your hand. 

Aerosol Cans:  Another no-no, especially those over 4 oz.  If you need hair spray, deodorant or anything else like that, buy it in Europe.

Tools:  When going through security, sometimes they put a box of confiscated materials on display.  I am always surprised to see hammers, pliers, files, etc. in those boxes.

Coins:  While not specifically banned by TSA or security, having lots of coins increases your chances of being flagged.

Here's a tip:  If you think anything you may be subject to confiscation or inspection by security or TSA, put those items in plastic bags for easy removal.  Sometimes if security finds even one tiny item in your suitcase they want to scrutinize further, they may make you empty out your ENTIRE suitcase for a full inspection.  And let me tell you, security is not really concerned if this full inspection will cause you to miss a connecting flight.  If you can remove these questionable items from a carry on before going through security, only these separate items will be inspected, not your whole bag.