The friend who makes an ordinary plan possible has contributed to more than the outing.

Ordinary plans have invisible machinery: somebody drove, somebody watched the children, somebody found the date that worked for four calendars. Without that, the outing simply does not happen, though it is easy to treat it as something that occurred by itself. The friend doing the arranging is often also the reason the group still sees each other.

Thank the organiser specifically rather than praising the day in general. Offer to take the next one, including the dull parts. And if you are always the one arranging, say so kindly out loud, because most people have never noticed.