For that go bag it is always good to have a metal detector, for years in the US Secret Service I used a very small metal detector/stud finder,it fit in my inner suit coat pocket. I keep my eyes open all the time for replacements. New stud finders are not always simple metal detectors, and as such can be hard to use as a metal detector.
I found this one today at Harbor Freight tools, it is an Cen Tech Model 97245 and cost 17$.. I have tested it and it will get the job done as well as work as weapons and evidence search tool. I will try and get a you tube up of how to use this metal detector as a mail bomb search device before the weekend.
They also had a hand wand search tool shown in the second picture was going for 39$ that is the lowest price I have seen for a weapons search system like this. If you are a guard force, corporate security, or Body Guard, this is a good tool to have one or two around.