Eh, if I had to buy coffee for the whole group after a flat, I definitely wouldn't be interested in riding with that group. I bring along my own tools and etc to repair a flat. I think every cyclist should be self-proficient on every ride. Bring everything you might need to fix a common mechanical on your own bike.

That being said, I never hesitate to offer assistance, patches, a tube, or use of my pump to any fellow cyclist.

Why not make the rule that if a rider gets a flat, he fixes it himself. If he can catch back up to the group that didn't wait for him, everyone pitches in to buy HIM a coffee.

That solves everyone's problem. **Of course, it'd be awfully rude to leave behind a newbie in the event of a flat.