Self aid kits and fragments of self-aid kits are like popcorn (they show up in a lot of places - even incidents). Many of us have 1000's of them.
Mass Self Aid kits are more desirable but rarer objects than can be found/earned as complete kits, but more likely, you'll get fragments of such from a number of sources. Of the two, the Mass Self Aid Kits (called MSAK) are the ones to chase and build a pipeline to obtain. Buildings in your city can make the fragments each day, and when the count gets to 30 in your inventory, they can be assembled.
That's where to put your energy.