Food
The production of food would have been particularly important immediately after the fall of the Empire because during the empires reign large areas of the planet could be magically enhanced and protected to allow food from off world to grow. Once the magical infrastructure failed these food production areas would revert to their natural states, killing off the diverse amount of imported species. Those who survived the early years after the fall survived by either switching to hardier native species or by replicating the proper conditions for other crops via different magical means that are more personally taxing.
One of the primary elements of growing outside crops is adjusting the local temperature. This can be accomplished by using magical materials that enhance the heating or cooling of devices they are attached to. While before the fall such magical contraptions were powered by piped in magical energy, these devices have to now be personally powered by mages.
Another important element of farming in the present day is gathering water. The water oceans of the world are almost entirely contained beneath it’s surface so that in order to access it one must pull it up from deep wells. This is one of the most important factors when determining where to build a settlement. While there are locations where water rises to the surface naturally through geysers in many cases people must transport the water manually. In some cases settlements have built magical pumps that utilize an allow that attracts water to pull it up to the surface through pipes.
Unfortunately that is all I have time for today. Hopefully I can continue this topic over the weekend.