Sonic,
I'm pleased you know why we all should carry whistles.
just remember that if you hear a whistle, look in the direction of the oncoming traffic, before you look at where the whistle is coming from.
You might want to think about scanners,very useful for knowing what's happening, especially when you're alone on post and haven't seen a car for 2 hours
Small digital camera. Can't be used on post, but can be well used during breaks.