Our troop usually does not charge adults who accompany the troop on campouts, unless of course their are an inordinate amount of adults going or the cost of the campout is prohibitive. On a normal, we're just going camping, weekend I don't pay the campout fee. I guess it helps to offset the cost of gas. LOL. If were going to some event while on the campout that would cost extra, I do pay. I really don't mind, I have just as much fun as the scouts.
On troop outings such as sporting events I pay my own way.