I was starting to have some pretty serious (as in happening ALL the TIME) issues with my 2 year old daughter as far as temper tantrums.
I tried finding a love and logic class near me but couldn't, so I went around to the local book stores and bought "Parenting with Love and Logic". That book was great but not so many specific ideas for pre-schoolers. So I ordered "Love and Logic Magic for Early Childhood: Practical Parenting from Birth to Six Years" from Amazon. It was hard getting enough alone time to read it but let me tell you, this book has been a total life changer. I've used techniques from it for tantrums, to food throwing, to jumping around on furniture and it's been pretty great. We aren't yet at the point of preventing the outbursts, but they get over with much more quickly.
So tantrums at stores. My kid's obsessed with M&M's and starts screaming when we go past a display of these. I tell her I'd be glad to give her some M&M's when she acts nice at the store. She keeps yelling so I tell her "Uh-Oh, So sad, I think you need some alone time." She's buckled into the cart. So I park it on the end cap of the aisle and say "It makes me so sad when you act ugly and yell like that at the store. I'll give you some alone time so you can think about acting nice at the store, and we'll start shopping again when you have a happy heart." Then I walk around the corner behind the cart where she can't see me but I can see her and reach her if anything happens. She sits there and stares. Then says MOMMY a couple of times and I come back and ask her if she's ready to act nice at the store and she says yes. And that's IT. 20-30 seconds and no more screaming about M&M's. I've only had to do that twice-it's been about a month since the last time that happened.
At home when she starts pitching a fit I do the same thing only I take her to her room and lay her on the floor. She screams all the way up until I lay her on the floor and walk away but then she goes quiet and eventually comes out of her room ready to act sweet.
In the car, I do the same thing, only I pull over to the side of the road and get out of the car. I've only had to do that a couple of times as well.
I wish I had found these books about a year ago. I've spent SO much money on tylenol.
Good luck, let us know what happens!