I was using a truck bag on a rack that clamped onto the seat post of my road bike. But I've just switched to a front rack handle bar bag. The new front bar bag is bigger, but I plan on roughly the same stuff.

For long randonneuring rides (and this varies depending on the length, time of year, weather forecast) (and I should mention I'm a junior Randonneur, so I'm still working out my load):
- Extra food
- Energy beverage mixes
- Some Tylenol
- Multi-tool
- Spare tube
- Pump
- Tire levers
- Patch kit
- Boot for repairing tire (I should jut start carrying a folding tire)
- Fiber-fix spare spoke
- Handy wipes
- Spare front light
- Spare rear light
- Rain jacket
- Zip ties
- Velcro straps
- The glasses I'm not using
- A pen
- A silver sharpie
- Money / ID / Credit card
- Zip lock bag
- Phone

If I'm just going out for a short ride (under 100 miles) I use an under seat pack with:
- Spare tube
- Pump
- Tire levers
- Patch Kit
- Multi tool
- Fiber-fix
- Pen
- I stick some food in my pockets. I just run on water or stuff from stores for beverages.
- I stick my phone in my pocket. I don't mind having stuff on my back for short rides, but I leave the pockets empty for short rides.