There is a plural for the noun lunch (lunches). It is not used very often. For example, you might hear, "Did everyone bring their lunch?" This 'lunch' is singular, referring to each person's meal. However, the answer to this question could use the plural. "Yes. Everyone's lunches are in the bus." 'Lunches' refers to everyone's meals as a group.

You could say for ex. "We have had, or taken many lunches together" Not common. Most people would say "We go to lunch together a lot"