You're at the ocean again and you need exactly 4 gallons of water this time. Unfortunately, all you have is an opaque 3-gallon jug and an opaque 5-gallon jug. What will you do?

Belated Bonus:

A man walks out of his house and heads due south one mile. He then turns left and heads due east one mile. Finally, he turns left and heads due north one mile and arrives back home. Who is this man?

Solutions:

Fill the 5 and pour into the 3. You will have 2 gallons left over in the 5. Pour these into the 3. Fill the 5 again and pour into the 3. Since the 3 already has 2 gallons in it, it will only fit 1 more. 4 gallons remain in the 5. I think this was featured in Die Hard.

The man is Santa Claus! He started at the North Pole. Alternatively, he could be someone living ~1.6 miles north of the South Pole. (Go south, take a circle around the South Pole, then go North. Exact distance is 1+ 1/(2π). )