I have a similar use case for Eldest Offspring. What I was putting together had to fit in a small cargo space underneath the deck of the trunk, in a bag for ease of transport on foot. Some differences:

• Several in our family have had medical training for treating traumatic injuries, so I included a small kit for that even though Eldest has not been so trained
• Included a small power bank, 12V to USB adapter and a spare charging cable
• Included a bottle of water
• Included a multitool with a bit kit
• Included an upgraded lug wrench to make tire changing easier
• Included a roll of self-fusing silicone tape
• Included an assortment of automotive fuses