Keeping them entertained is a great tip! I find that having a variety of engaging activities, especially ones that can be done independently, helps my little one stay occupied when we're out and about.
The calm-down corner is a brilliant idea - creating a cozy and inviting space for kids to self-regulate is so beneficial, and I love the idea of decorating it together too. Making it a fun, positive experience can really encourage children to use this strategy when they're feeling overwhelmed.
I also find success in preparing my child in advance for transitions or changes in plans. Giving them plenty of warning and explaining what's coming next helps them prepare and reduces the likelihood of unexpected meltdowns. Even if we're just running a quick errand, I'll often give a 5-minute warning before leaving a fun activity so they can mentally prepare.
For younger kids, having a few small toys or books on hand that are only brought out during "emergency" situations can be a lifesaver. That combined with your snacks idea is bound to buy you some time and keep everyone's spirits up!
It's also a good reminder to ensure we have our own calming strategies in place - deep breathing always helps me stay level-headed when the kids are having a tough time! I find keeping a level head, even when things get chaotic, helps the whole family remain calmer.
Those are my quick tips - would love to hear more of your insights and any other parent's secrets too!