backpack with hydration bladder – only put water in it or you will have to clean it regularly
water bottle with some sort of electrolyte or energy drink (dishwasher safe)
1 spare tube (sometimes one is not enough)
1 patch kit
tire levers (at least 2)
multi-tool, preferably one with a chain breaker, Allen wrenches to fit all bolts on your bike and screwdrivers to fit derailleur adjustment screws
small handlebar LED light or small Mag light for backpack
spare chain links and SRAM powerlink – make sure you get the right one for your drivetrain as they have different ones for 7, 8 and 9 speed.
spare derailleur hanger (if your bike has a replaceable hanger)
spare chain ring bolt
spare spoke nipple
rag
chain lube
small first aid kit
tire pump
small length of duct tape (wrapped around tire pump)
zip ties (varying lengths)
personal ID and medical information
cell phone