One thing that I haven't seen: work more closely with Obama's transitional economics team than an outgoing president usually does.
Everything I've seen about Bush and the transition indicates that he has been entirely classy. But right now, classy is not enough. The more publicly he is seen to coordinate with the Obama team, the more reassuring it will be to markets. And it's up to the Bush administration to push this--the Obama team can't do so without looking panicky, and spreading that panic to others.