Many of the systems designed for use in space can be adapted for use on Earth. The main hurdle for this is cost. These systems are optimized for space where the scale is much smaller. However, since this technology already exists, ways to make these systems more efficient and cost effective could most probably be created in the near future.
Water reclamation systems.
Space has nothing. It provides nothing in the way of resources or utilities. Everything that makes living in space possible must be sent up from Earth. We have slowly been developing technologies that make life in space self-sufficient. For example, until 2010, water used to arrive at the ISS in duffel bags. Now, there is a purification system that allows astronauts to reclaim more than 4800 liters. The water requirement for an average human is about 4 liters per day. Therefore, the same water reclaimed from sweat and urine could last for years. The space station however is a closed system, and results would be very different on Earth where it is not possible to preserve all water. But this tech shows huge promise and with some refining, could sustain populations in arid regions for a long time.
Agriculture to deal with Malnutrition.
On the ISS, plants are being grown in small numbers. While this is not enough for sustainability, it gives us time to monitor each plant individually and possibly, provide us with an optimal method of growing each type of crop. This could significantly increase yield.