Coping with toddler tantrums??

How do you cope with toddler tantrums in public? I refuse to take my doctor with me to doctors appointments or supermarkets because she will throw a tantrum at some point! And I have a newborn so I find it really daunting now! I can’t tell her to stop or anything (well I try) because she can’t talk yet so she can’t really understand what I’m saying. (Although sometimes I think she does! When my husband asks me to pop to the shop for something I panic because I can’t let my toddler walk cos she will keep trying to run around and grab things off the shelf! And she screams in the double buggy! 😩😩