When deciding what tools are reasonably required to be allowed airside i normally question the engineer as to what he is actually doing on the aircraft, in most cases engineers have far more tools than they really need, these tools are not only a security risk there a FOD risk also only recently when carrying out a walk round check i found a large monkey wrench left under a aircraft by a careless engineer, imagine the consequences of something like that flying into a engine or being found by a terrorist.
In most cases a torch screwdriver, adjustable spanner and a pair of pliers are more then enough if the engineer needs more than that he should have a written memo from his supervisor explaining to the security officer involved the reasons why.