These are usually in the form of medical supplies that can be used to treat different minor injuries while in the field. It is important to know that some items can double in use for this category increasing the versatility of your four essentials kit. Generally, some customization is made to your traditional first aid kit to match the needs and environment of each activity. An additional consideration is the climate and environment, and what clothing or protective items would apply. An extra clothing layer or windbreaker could help avoid hypothermia and in contrast, sunscreen or bug spray could be added to this segment for increased quality of life and to counteract potentially dangerous sun burns or bug bites. An item to strongly consider is some form of tick removal (specific tick removal devices exist but tweezers can work as well.)
first aid supplies
extra food
water purification system
pain relief
a couple ideas of things to add to your kit.