I try my best to obey all firearms laws. I enjoy the fact that we, as a group, are among the most law abiding citizens. And sure, there are some cases where I must disarm to shop for what I need, if the store is posted. And I don't like doing it.
However, in most cases I avoid doing business, wherever possible, with stores that clearly don't want me (a legally armed citizen) there. If one gas station/stop-and-rob is posted, I give my money to the Speedway that is not posted across the street - even if I never go inside. If one sandwich shop posts, I give my business to another. Been doing it for several years, as have many folks I know who carry.
If the store is just following corporate policy/procedures, there may not be a lot that can be done. A smaller business may reconsider if they receive enough emails or "no guns, no money" cards explaining that they lose "X" amount of business from me every week that I give to their competitors.
In any case, I just feel good knowing that I'm denying them revenue in return for them posting a sign saying they don't want my business.