I am in agreement with Tolik. In the US, unless there is a total power grid collapse via CME or EMP attack, the Govt will re-establish control, at least in urban ares, relatively quickly.
Again, what is the nature of the SHTF event? If a pandemic, and one is forced to stay in your home to avoid infection ( see movie Contagion ) then food and clean water are essential, as are weapons to defend ones household/retreat. I have water filtration system and well to trade, as well as extra food and possibly ammo.
But the circumstances I might initiate trade would vary, balancing OPSEC and a determination to keep as low a profile as possible about what I have stored up as to avoid being a target. I have lots of soap and med supplies, like Ibuprofen. hygiene would be important.