It depends on how into it you can and want to get. Obviously, a full kevlar helmet, gas mask, and chem suit is going to offer the most protection for the widest range of situations. However, they might not be the best choice if you're trying to stay somewhat incognito.

I mean, I could throw that bump cap on to protect my head from rocks and debris, while still blending right in with a crowd trying to get away from a riot or terrorist attack or whatever. On the other hand, if I'm the only guy in the crowd with military surplus gear on, it might be cause for me to be singled out as an instigator or part of the terror plot. I might also end up having a problem with someone noticing what I'm wearing, and then deciding they need it more than I do.

For me, I figure it's best to have some level of protection while, at the same time, being able to blend in as much as possible. That allows me the most options for the widest range of situations.

I mean, I could take my bag and walk throughout most cities in the U.S. with it no problem. Only items that might cause a stir are the multi-tool, swiss army knife, and pliers/pry bar....which are fairly ubiquitous, but can be ditched if I need to get through a checkpoint. Otherwise, my kit is pretty similar to what was given to MTA workers after 9/11, just with higher quality components.

On the other hand, the military surplus items might cause some issues, and they're a bit bulkier/more difficult to carry, as well as more difficult to ditch.