When your first baby is born and you read everything there is to read about bringing up baby, this topic comes up a lot. If you're paying attention you'll soon notice that most of these techniques are orally fixated - thumbs, pacifiers, fingers - so it's no wonder many of us grow up still self soothing by sticking something into our mouths.
None of these foods are even remotely good for us, either. Have you ever heard of carrot as comfort food? I didn't think so. "Have a spinach salad, dear. It always makes me feel better." Nope, you'll never hear that one.
I just looked it up (surprise!) and found some great ideas for self soothing as a bigger person. It's about sensory experience drowning out the little voices in your head. Here are a few of the ideas, but they're mostly paraphrased from this site: psyke.org.
Walk in a beautiful place, listen to music that makes you feel good, read a book, knit (well, I don't know how they missed that one, but it works for me, so in it goes), bake bread, drink herbal tea, put whipped cream on fruit, take a bubble bath, put clean sheets on the bed, hug someone. Learn to use all of your senses to calm yourself down.
Alrighty, then, if you need me, you'll find me taking a bubble bath while listening to music, burning scented candles, drinking herbal (lemon, I think) tea, and reading a book (not a library book, though, since I'm in the tub in this scenario).