on my light and fast (nothing I do is really fast) commuter I have

air pump
extra tube
light/front and rear
saddlebag
computer mount
water bottle
tire tools


on my daily use bike I have all that plus a back rack, panniers, lock, more tools. I carry lunch and clothes and other work stuff on a daily basis. And on the clothes at work reccommendation, I always keep everything I need at work, in case I forget everything. Which could happen.