I learned about this from some 4th grade teachers when I was subbing at their school last week. It is a great visual image to remember when learning to convert cups to pints to quarts to gallons and so forth.
Some people call this "Mr. G" and others call him "Mr. Gallon." Call it whatever you'd like but I tell you, IT WORKS!
Draw a giant G (for gallon). Within the G, draw 4 Q's (for quarts). Get it? Four quarts in a gallon. Draw 2 P's in each Q. That means there are two pints in each quart. Inside each P, draw two C's. So the kids can easily see that there are 2 cups in each pint, 2 pints in each quart, 4 quarts in each gallon. They can solve a myriad of word problems using this simple memorization trick.
Here are some websites that have a story to go with this memorization trick. THIS WEBSITE has a fun story about the Gallon Kingdom and also a picture of Mr. Gallon that works well too. THIS OTHER WEBSITE tells about the Kingdom of Gallon too with a slight variation from the other website's tale.
The kids all have the chart memorized and when they got their tests on unit conversion and word problems, I saw them writing this on the top of their papers to help them visualize it and more easily convert throughout the test.