If someone approached you, politely and respectfully, in a grocery store parking lot, and asked you if you would please help ...?

I've often offered to buy some basic groceries for parking lot panhandlers and all but one of them turned me down. If they won't take food, only cash, you can be pretty sure they don't want that money for sustenance (but for recreation...feeding an addiction).

 If someone approached me at the DOOR of the grocery store, yes I would do whatever I thought i could to help them. When you are walking to your car and someone approaches you I find that unsafe. At least at the door other people could see your interaction. Just be safe! 

I don't believe there's a "polite" way to ask a stranger to pay for your things or give you money. I always say NO when I am asked.

A lot of these individuals are convicted felons who can't find work or lodging because they're in and out of prison. That "nice and polite" man that you give money to might have raped a five year old.

There are social programs that offer the bare necessities and I don't feel that "beggars" are entitled to more than that. I always say:

There are so many people living in the streets and broke, so why don't they get together in small groups and help each other? They know better than to trust each other, that's why.

I would say sorry that I can not help you. it is like the people begging for money. my late husband would give this woman some money, thinking she needed food and she took the money and had her nails done and got a haircut. I had told him not to give them money anymore. many come out of a car and beg for money, they had to have money for the gas in the tank

If I felt the person was genuine, I would have joined him back in the store and physically buy what I was willing to donate to him and pay for it myself. I would not give my money to him.

I would probably take him back into the store with me, and buy some basic staples for him.  I wouldn't give him money.  This happens all of the time in Dallas.  Right after Hurricane Katrina, there were literally hundreds of refugees roaming the streets, begging.  Some of them were obviously very poor and looked as if they needed help.  They were apologetic about their situation.  Then there were the hostile and aggressive ones who wouldn't take groceries. They demanded money and they would get in a person's face and sometimes they were threatening.  The police warned citizens to direct them to homeless shelters and not give them anything.  The  crime rate in Dallas rose by 30% that year, and it hasn't  decreased in any  way.  We are now 3rd in the nation for having homicides. 

i might pay for the stuff but i wouldnt give him money

Sombra, you haven't told us exactly what he wanted. In comments you've said he just wanted ingredients to make sandwiches. Yes, fine: but did he want you to BUY the ingredients for him, or did he want you to give him the money to buy them for himself?

THIS is the crux of the matter, and your post hasn't made it clear. 'Covering the cost' isn't specific: did he want the loaf of bread, or did he want the money to buy it?

Would listen to gut instinct, and either accompany the individual back into the grocery store and buy specific items, or suggest a local food bank/community house/welfare offices.

Since I truly don't have much on me, I'd have to decline, and that would be my honest answer. Unless the person talked to you after you got your shopping done, it could be, probably a scam.