Credit cards

puzzle me. I don't own one. 
I know I may need to own one eventually but, right now, the Senior Cat and I share the bills. We pay them as they come in because we are fortunate enough to be able to do do that. 
The Senior Cat has a credit card but he almost never uses it. He doesn't like doing that. He likes to know he is not in debt to anyone - even the bank.  
I know his means of paying bills is old fashioned but it is the way  he feels comfortable about it. I also know that, when the time comes, I'll probably go direct debit for as many things as possible - something he steadfastly refuses to do.
At present I use a debit card - and put a limited amount of money on that at regular intervals. 
It all works - sort of. At least we pay the bills on time.
So yesterday I watched - or rather, tried not to watch - as the woman ahead of me in the supermarket tried first one credit card and then another...and then another...before she found one with which she could buy her groceries. I found it quite terrifying the way she seemed to be not in the least bit concerned about the fact that, "Oh that one's maxed out" and "I haven't enough left in that one". 
I couldn't help wondering what the limit on them was and, of even more concern, how she intended to pay off what was on them. Perhaps she did have a large income and it really didn't bother her? I have no idea. It was none of my business anyway.
But it did make me think about paying my own bills and paying them on time. I've never had a big income. I have managed on what, for most people, would be below the poverty line for years. I can do it because I don't run a car. I buy most of my clothes in the charity shop and we almost never go out for meals or entertainment. It really doesn't bother me but it will if it reaches the point where I can't pay the bills. 
It makes me wonder whether I will ever be in what, for me, would be an excruciatingly embarrassing position - of not being able to pay for essential groceries. That would bother me. 
I wonder what that woman was thinking. She didn't appear to be concerned or embarrassed but perhaps she was underneath.
I pretended not to notice.