I am a very comprehensive beach packer (some might say it's overpacking, I prefer to think of it as being thoughtful). The first couple (few?) years are really hard when you're figuring it out. Now I have a saved packing list that I can pull up and update/adjust year after year, which has made it easier (I use Evernote, but any number of tools will work for this).
It's also gotten easier as my kids have gotten older - we needed a lot more specific stuff for 2 year olds than we need for 5 year olds (feeding, diapers, pack & plays, boosters, etc. etc.). At a certain point they become more like extra bodies who need more standard supplies vs. these creatures with all of their own variations of "stuff."
I find large plastic tubs to be good for packing kitchen/grocery stuff into. We also have a (soft, fabric) car top carrier). If you have other family staying with you, see if anyone wants to be in charge of a meal or can bring helpful supplies for the house (tissue boxes? laundry detergent?) or for the beach (chairs, towels, etc.). Make sure everyone knows what they need to bring for themselves (I now tell everyone they're on point for their own bedrooms and bathrooms, beach towels, etc.)
Generally, I try to make sure that I can get through at least the first 1-2 days without going to the grocery store. It's already been a long day of travel, and in many beach towns, the weekend days are kind of crazy. By Monday, I'm eager to get to the store for a trip on my own