hey, at least your supermarket gives you an employee discount. I don't even get an employee discount.
we have "club cards" like what ponyone described. and we can get fired for letting a customer use our cards. we technically can't even let a customer use another customer's club card (though we let that one slip a lot more when it's obvious that the two people are relatives or friends)
it doesn't really matter though. our club cards are tied to your phone number, so you just punch in your phone number on the little machine where you swipe your credit card and it's the same as having the card. and even if you don't have that, you can just ask for an application for a club card. we can give you the card right away to use immidiately, and you can just take the application home saying you'll "bring it back later" and just never fill it out. of course, then your phone number won't be linked to it, and if you do lose it, then you won't have the benefit of typing in the phone number.
anyway, enough ranting from me. I'm sorry to hear that you were fired. but there are so many better jobs out there then working at a grocery store. just about everything except fast food is better...