This is going to be long and probably very inaccurate. We will assume that since the cells are filled with water, they have a similar density of 1000kg/m^3. One lightyear is 1E15 ly, and if I assume you are discussing the observable universe with its expanded size to this day, I will assume it has a radius of around 4E10 ly, so thus its 4E25 meters in radius. The volume of a sphere is roughly 4 times the radius cubed, so its 16E75 or about 2E76 m^3 and 2E79 kg. E=MC^2, so 9E18J/kg or 18e97 or 2E98J. We will say a kilogram of water can be boiled by something in the order of 1E4 Joules, so we Have 2E94 kg of water. A kg of water is roughly 50 moles, so we have 1E96 moles of water, which can support 1E95 moles of glucose. I would guess something like 1E5 Joules to react a mole of glucose, so we have 1E100 Joules to power the homes. I would guess a home consumes about 3000W*3600*24=3E3*4E3*2E1=24E7= 2E8J. I will also assume for consistency this is year of energy, so more like 8E11J per year. Thus we have 1E88 american households. Of course some have significantly more and significantly less, but I would guess the average is something in the order of $2000. per person, so we have 1E91 dollars. Thus I would guess 90 as my Fermi answer for the number of whoppers. (plus or minus many powers, I am sure)
How many meters of film would a professional photographer use in his or her career assuming that he or she uses only film and never digital?