Maybe some kind of bond between your survivors? The more supply runs/ missions 2 community members run together starts to build that bond between them grants small to larger buffs whenever they’re together like a boost to stamina or health. At max level grants a determination trait when active gives both a large health boost to make it back together. If one dies the other is hit with a major debuff for a long time maybe make the survivor suffer survivors guilt or become more distant to the community afterwards for a while. Assign a mission to go and kill their partners zombie if it hasn’t already been done so they can start healing. It would give people the option to add more lore ideas in their head cannon like say these 2 were best friends/lovers/partners whatever you want in your community