There are four different types of resources: money, building materials, ammunition (ammo) and medicine. In addition to money, you need building materials for building from level 11 on. You need ammunition (ammo)  to train characters from level 10 upwards and medicine to heal your characters from level 4 on. 

You unlock building materials by reaching level 10 of your clubhouse. This also unlocks a new part of your district. You unlock ammunition (ammo) by upgrading the military depot (only possible if you have unlocked building materials). To upgrade the military depot, you need a character with level 8 and the Pawnshop. 

To produce medicine, you need to have a character with level 4 and upgrade the doctor.