I also carry a freezer ziplock bag with bandaids/pads and a bit of tape. I put my phone in there so it does not get drenched with sweat in my jersey pocket.

For roadies, I also carry these small one time use super glue. It can be used in emergencies to put a patch on tubular tires. (Out side of the tire just to get you home). But it also can be used for mtb on a stubborn hole on the topside of the tire. The stuff dries really fast and hard.

Your also carrying water and food... a GPS device... (I know this post was more for bike repair)