I am one that HAS had success in walking up and getting soup and pretzel bread at the hostess stand
I have also been denied though. The couple of times I was successful were right when the restaurant opened in the morning and mid afternoon-ish. I don't like steak...so when we do go to sit down, I really just get the soup and a salad, so I love when I have success taking it out!
IMHO...doesn't hurt to ask, worst they can do is say no.

IMHO...doesn't hurt to ask, worst they can do is say no.