Like many people, we keep a grocery list on the refrigerator, adding to it as we need things. Unlike most people, though, all the items on our grocery list start with the same letter. It all started when one time, by pure chance, the first couple of items on the list started with the same letter. Whoever continued the list started manipulating the names of the rest of the items so that they continued the pattern. Thus was born our tradition: whatever letter starts the first item that happens to go on the list is the letter that must be used to start every other item.
For example, eggs have been, at various times, chicken eggs, poultry eggs, avian eggs, or ovoid eggs, depending on the initial letter (this last one is a little redundant, since the definition of ovoid is "egg shaped.") Milk has gone by such names as cow's milk, lowfat milk, one percent milk, bottles of milk, and, my personal favorite, bovine liquid. It makes for some interesting situations when one person is standing in the grocery store trying to figure out what an item that someone else added to the list is supposed to be.
As with many such traditions, there are rules, but the rules are simple: no manipulating the first item on the list to get the letter you want, and no repeating a modifier. For example, if you've used "bottle of dish detergent," you can't then use "bottle of cranberry juice."
Some letters are easier than others. We've discovered that 'C' is a pretty good letter; besides all the wonderful foods that start with 'C' (cheese, Cheerios, chicken, etc) there are lots of good adjectives and some useful container words, such as can or case. 'D' is a surprisingly hard letter, as we discovered when our recent holiday shopping list ended up starting with a 'D', and we had items on our list such as drops of chocolate (chocolate chips), dough flour: white, dairy sticks (butter), diamond-like crystals of sweetness (sugar), deciduous tree fruit pie (frozen apple pie), and dead chicken in shells (eggs).
For those of us who are writers or editors, in one way or another, words are our tools and anything we can do to sharpen the tools helps us. Wordplay such as this is a great way to increase our vocabulary and build our skills at using words in new and unusual ways. Many times we've had to consult a dictionary or thesaurus to come up with appropriate words, and creativity plays a big component as well. But more than anything, it's just a fun and silly tradition that we enjoy doing together as a family.