For me it would be dining. While your appetite and preferences on the day might change, I find it useful to look at menus for the flight(s), as well as that for the lounge, beforehand - to get an idea of what I may eat and when. Emirates is good at sharing menus in advance for flights and the DXB lounges.
Note that most cooked meals in the lounge take around 10-15 minutes to prepare (in my experience) so knowing in advance can help. For reference, on somewhat shorter connections I've ordered then used the bathroom and/or bought something from the duty free spot and returned in time for the meal.
If eating not a priority then checking out the spa is an option.