I just had an idea which may help people who are nervous about getting diapers in real life/being seen getting diapers. What you'd do is make it out to be a game where you're trying get the weirdest look from the cashier. One of the things you could get would be: some kool-aid mix, a ball of twine, motor oil, a pack of straws and some diapers.
By making it into a game, it would relieve the stressfulness of the situation, and would be an easy excuse if you saw anyone you knew.
feel free to input your thoughts of the idea.