When I go to dinner with some friends, each of us pays for exactly what we ordered. With other friends, we split the bill evenly even if one person's meal is slightly more expensive than the other's, figuring things even out over time. And with others, we alternate who pays. With this last option, in theory one of us usually owes the other a meal – some might call this a form of social debt.
Usually I think of debt as something that I'd like to pay off quickly, but in this context debt can be an good excuse for us to share another meal together. I like that the person who wants to pay the next time is eager to organize the next meal.
In one-on-one settings, this is my preference. It's too bad this gets impractical with larger groups.