When "friends" split a check, advice needed on getting them to fair share

[Michael]

We have a similar thing happen when a group goes out after church, but with us it's families. There are several families with multiple children and a couple of us who are just couples. At the end of the first time that we joined the group, somebody said we just split the check. That first time we payed an extra $20 over what we ate and I grumbled but my dear wife pointed out that these are friends and they are worth an extra $20. She was right. But, I also now do go ahead and get a more sumptuous meal than I normally would and just try not to worry about it.