Ladies have it harder. For my 20-mile round trip I take:
Repair stuff:
Pump
Inner tube
Repair kit
Tyre levers
Clothes:
Trousers/skirt
Top
Bra (yes I need an alternative to the sports bra)
Spare socks
Waterproof jacket
Toiletries:
Deodorant
Facial wipes
Moisturiser
Food:
Energy bar
Water (on the frame)
Security:
D-Lock and loop
Occasional extras:
Music for rehearsals
DVDs to lend to friends
Food shopping on the way home etc etc etc
I bring my shoes and towel on Mondays, leave them at work in the week, and take them home on Fridays. Plus there's my wallet, keys and phone.
That's why ladies are slower I reckon, the extra weight!