You, my friend, are a pressure cooker waiting to burst. Here's what you need: seek out professional help to deal with your anger. You're right: bottling up all of these emotions is bad for you, your nerves, and your heart.
But what is causing you to feel so angry in the first place? Clearly not everyone else in the grocery store harbors your levels of consternation. You must learn to relax when in public — let go of the stress.
Eliminate this response you're having, and you'll find yourself a much happier man.