you must come up with any four items that could be found at a store like, say, Fred Meyer. (This is a store that has a wide variety of groceries, but also has sporting goods, cosmetics, electronic equipment, clothing, etc. You get the idea.) The point is that the four items be innocuous in and of themselves, but in combination would completely freak out the checkout clerk, or at least make him/her wonder what in the hell you've got planned for the evening.
There's really only one definitive answer to this, and anyone who's seen the movie "Very Bad Things" knows this: