Spare battery for the camera and maybe a cigarette lighter charger for said battery(s)...in case your navigator runs the battery down you can switch quickly and we won't miss but a beat of the picture taking.
I may be mostly alone on this one, but I was not aware that 987s did not come with spares...now I'm kinda glad I went with an oldie...how'd Porsche get away with th---nevermind, I should know better than to finsh that question...
BTW, what car is that reflected in your car's paint? I know that's no 944...just curious.