Entry: Campbell's Soup Can

   A regular soup can is 6.5cm wide and 9.8cm tall, while the average bicycle is 90cm tall. Judging from the picture, the circumference of the enlarged soup can is roughly 2 bicycle heights. However, due to the downward angle of the camera shot and guessing  how much of the can is buried, I will add an extra half of a bicycle.

   Therefore this can has a circumference of 225cm. A regular can has a circumference of 6.5cm. Therefore this can's circumference is 225/6.5 or 34.6 times bigger. If we extrapolate that, the can should be 34.6 times taller. Since 34.6 x 9.8 is 339.23, the large can should have a height (in the picture's case, a length) of 339.23cm.

The volume of this tank should be π x 112.5cm^2 x 339.23cm or 13.481 million cm^3. This equates to 3,561 gallons. This seems smaller 
than I would have guessed, so I will try a new method using the bicycles length, which might be more 
consistent between bicycles. I would judge the can to be 2 and four fifths bicycle lengths long. The 
average bicycle is 180cm long.

Therefore this can has a height (length from the picture's perspective) of 180*14/5 or 504cm (this is much larger than the previous method's height of 339cm). A height of 504cm compared to a normal can's height of 9.8cm making it 504/9.8 or 51.43 times bigger. The circumference of the can would therefore be 51.43 x 6.5cm or 334.3cm. The volume of this large can would be π x 167cm^2 x 504cm or 44.12 million cm^3 or 11,655 gallons.

This is an interesting question because the answer will depend on how interested you are in the question.
You could simply eye-ball the size of the can and try to work it out from that (which is acceptable), but
you can also factor in the angle of the camera, the distance that the bike is away from the can, how much
of the can is buried, etc. No one will have the same answer.

I think the most interesting follow up question is to ask: "If the can is a normal can, then what are the
dimensions of the bicycle?