First: you'd have needed very sensitive scales to measure a difference between the total mass of bike-plus-food-plus-you and bike-plus-you-with-food-inside.

Second: the loss of the mass of the food and drink wouldn't stop the bike rolling (though halting to release ballast might have made it awkward to re-start). In fact, it's possible that the extra mass would slow the bike down due to extra friction - particularly if the tyres were a bit soft.

I'm trying to imagine where else you could lose mass from the system (if you ate the food and drank the water) and can only come up with sweat and increased exhalation of the waste gases of respiration. When you are dehydrated and still hot, drinking copious amounts of water certainly allows extra sweating. Assuming the sweat is able to evaporate then it would be lost from the "system" (i.e. the total of you-bike-food-water). Eating normally sets off an increase in metabolic rate because the food must be digested and absorbed, which requires an input of energy, but this is not going to tax your body too much while you are sitting on a free-wheeling bike. If the first part of the bike ride was very vigorous then your muscles would be undergoing some maintenance and cleaning-out routines. This might require the consumption of some energy, but might  yield some energy if lactate is oxidised. Either way, the net loss of mass through increased CO2 exhalation would be minuscule.

I'm sure you had plenty of time to enjoy your surroundings anyway!

Downwards gravity is about 9.8 m/s/s. That means that if you fall straight down without any friction you'd be falling with a downwards speed of about 10 meters per second after falling a second.

As we can all remember a kilo of feathers has the same gravity as a kilo of lead.

Riding your bike downhill has nothing to do with the total weight but everything to do with the friction the wheels put on the ground and the friction the air give to the person riding the bike.

My personal opinion is that if you loose weight you'll probably go a bit faster because your wheels will be having less friction on the road, depending on how hard your wheels are this might change a couple of % of total riding time.

Let us view this situation from first priciples.

A falling body will accelerate at 9.8m/s/s until the frictional drag (force) equals the "force of gravity"(F=ma or F=mg). This is called "terminal velocity".

So notice that the mass of the object is relevant or another way of thinking about it, is that the heavier object has more "potential energy" (=mgh).

Take an extreme example of a feather falling (obviously very slowly) - now add a small lead weight (which does not significantly add more skin drag/friction), the feather will reach a much higher terminal velocity QED.

I have sacrificed pedantry for succintness, but if one wishes for a more rigorous and interesting (but not totally analogous) approach see

http://en.wikipedia.org/wiki/Lift-to-drag_ratio

Bear in mind that glider (sailplane) pilots will intentionally (though counter-intuitively) add mass in the form of water to their aircraft when the regions of uplift are significantly greater than best still air sink rate of their aircraft.

http://en.wikipedia.org/wiki/Glider_%28sailplane%29

That's a well-made point, in answer to Jon's anecdote, but if you drop a weight, with a weight attached, you don't get much increase in velocity (I would say "any increase", but there's always a chance). The original question doesn't really suggest air-resistance being a major factor - it sounds like the bike was barely moving.