Pre-ride checklist:
1. Bike [i.e. it's in the car with both wheels and a seat]
2. Pack [I can usually tell by feel how much water is in there - if I'm wrong I'm thirsty]
3. Helmet
4. Shoes
5. Helmet [I hate riding without a helmet]
6. Shoes [I hate riding without bike shoes]
7. Gloves
8. Bug spray [they fly faster than I can ride, and can easily bite through jerseys]
9. Slurpee money
10. Sunglasses [$2000 for laser eye surgery - I'm protecting my assets]
11. Wife [optional]
12. Wife's stuff [see items 1-10]
13. Guidebook [optional - I've done most of the rides in the area, so this doesn't get used too much anymore]
14. Cell phone

That's for a ride that's 40km or less [i.e. 4 hours or less]. If the ride is "epic" [i.e. no rescue, just recovery], I'll throw in a first aid kit, double or triple the water, plenty of high fat/sugar food, and something to start a fire with.