G.B.
He and his co-workers have bonded and they are working closer due to this lunch time get together. I think that telling him how you fell is important but as for going out to lunch...that's a given for me. He looks poor and cheap if he takes his lunch. That's what everyone who takes their own lunch looks like. Either they can't afford to go spend a couple of bucks for lunch or they are just a cheapskate kind of person.
I know that women are more likely to do this but men, no, they should never take their lunch.
I suggest you sit down and go over the budget with him and look at just how much he's spending. If he can decide to get a lesser priced item, not salad or something but maybe not a T-Bone...that's what I mean...then try to understand this is work related and that you have some say in it but he is going to need to have enough money to do this each day.
Just try to work together so you can get the cost down a little if that will make you feel better. I would think that cutting it down some but not a lot would not be hard.