Why is this piece in a national newspaper?
This is not about veteran disrespect, is about you throwing a fit when things don't go your way. You had so many options to resolve the situation, yet you insisted on using your father to solve your problem (you said you only wanted to take HIM shopping - if you only purchased his stuff the cash would have probably been enough). 
Costco has a store policy - many times I see non-members ahead of me in the line being told they can't pay (but their members companion can). Among the stores I shop at I find them the best at customer service.
As Remembrance day is very important to your dad (and to you I assume) what are you doing out, shopping at 10am on Nov 11? If needed to be somewhere at 11 I wouldn't dream pulling in the Costco parking lot at 10. And that's without having an elderly man with me.

Thank your dad for his service.