We just got back last night from Mexico so I thought I'd add my .02 while it's fresh.
We are a family of 5. I don't think we overpack but I don't want to buy everything from sunscreen to shampoo. I bring mini sizes.
First thing we do after checking in is to head to the grocery store....actually during the last 10 yrs of timesharing my husband has done the grocery shopping

We usually just get milk, cereals, eggs, yogerts, bread etc for breakfast, sandwhich making stuff, cheeses, kid drinks, water, snacks, premade salads & chicken. I am so happy when we're on vacation because I do no cooking! We always eat breakfast in. Usually we eat a late lunch and snack later in the evening or go out for dinner but rarely eat all three meals in or out.
One thing that others mentioned that I wish I brought this time especially since we didn't have luggage fees, was a small non stick pan. We only cooked breakfast but it would've been worth not scrapping the heck out of the pan and ruining eggs... I've brought one a couple of times but usually don't remember and wish we had.
Uncouth warning...: WHY don't most resorts (at least that we've stayed at) have exhaust vents in their bathrooms? We always bring matches, does wonders in a bathroom.....
-a soft side cooler
-a canvas bag and/or backpack...because no matter what we have stuff to lug around
-I've never brought dishsoap and never needed it. You can always call ahead and ask what they provide.
-laundry soap & stain stick (remember 3 kids!)
-I use ziplocks for everything from toiletries, jewelry, stinky shells to leftovers
-Aloe because WHEREVER we go, WHATEVER time of year, one of us gets sunburned!
-bug spray
-have to have coffee before anything else! I bring one of those air sucked out coffee bricks & filters
Travelling with kids is a whole lot different than just two adults. When my hubby and I go alone, we can get away with carry-ons only. We've gone on several trips when all 5 of us had a small carry on.... It CAN be done. Just depends on where and when you're going.