Sometimes you do stuff like that for a co-writer. You call ahead to see what they'd like from Starbucks. You don't use mayo on your sandwich, cause you know it makes them nauseous. I've babysat a few times, and I've driven through snow and ice to keep an appointment. I've let people off the hook when they've stood me up (and I've needed that kind of grace from others more than once). Once I flew to Oklahoma so I could ride back to Nashville with Dave Clark. That's maybe the craziest thing I've ever done for a co-writer. If you've done much co-writing, you could probably tell a few war stories about stuff you've done for people you write with.
Though some things fall in the category of "above and beyond," most fall under "common courtesy." There are a few things co-writers have a right to expect from each other:
1. Presence and preparation. Show up with ideas and be fully engaged in the co-write.
2. Honesty and kindness. Speak up and say what you really think, but make the room a safe place where everyone can "dare to suck."
3. Confidentiality. What happens in the writing room, stays there.
4. Effort during the co-write and follow-through after it.
I kind of think that almost any issue that comes up between co-writers can be solved by referring back to these four guidelines. Then again, I guess you could say the same thing about almost any issue that comes up between people.