The outbox my server produces contains literally all activities from the user addressed publicly, without regard to their type.
WRT a wall, I suppose you could include activities from other users there if you chose to; it’s a novel case. I think I would create a wall collection instead.
WRT photos, see above. If the add activity is addressed publicly, then I’d put it into the outbox. If you choose not to address it publicly, then I wouldn’t.
WRT groups, I plan to put items into the group outbox that will help new members synchronize to the group’s current state.