Tools. I have two extra tubes, a patch kit, tire levers, and tire boots. I have a crank bros multi tool (chain break, hexes, spoke wrench, Philips and flat head) and a small adjustable wrench. Mostly use those to adjust brakes and my seat post / saddle. I also have chain lube and a small letherman tool. Most of this stuff is packed on my handlebar bag, for easy access. I carry the letherman in my pocket, mostly from force of habit of always having a pocket knife on me.