You can go with anyone you want to any of these places fast casual places. Stand in line together. Who cares!!! Just order separately and pay separately. Make the observations that need to be made. Your order does not take any longer or shorter amount of time because you know someone in line. You go by yourself and there is a person in line ahead of you. Do you think that time changes because now that person in line ahead of you is your friend? If you are truly worried about it, then let your friend order and you can go up to the counter a couple minutes later and order your food. But do not, not go with someone because you think you have to go alone. That is nonsense. You make the required observations. If you cannot do that because you brought a friend/spouse/whatever, then you are not that detail-oriented to begin with. Only exception would be if you tried to bring toddlers/infants with you that would comprise your attention.
I go to many food places that are shops and if my wife is with me, she is ordering separately and paying separately.
I understand it's a different situation with a sit down restaurant and table size. I'm not suggesting it there.