So for the meat and cheeses (for sandwiches), I freeze and put into a soft sided cooler.
Pack water bottles, but not soda (can buy the liters pretty cheap at the resort, but the water bottles kill us).
I don't bring bread either - again at resort.
But then I buy pringles (in container) potatoe chips, cheese sticks, mayo, salt / pepper, cereal (buy milk there), and other snack foods. They seem to make it okay. Also, I put in sandwich bags to break up snacks to smaller portions for the park, and leftovers.
Throw in liquid laundry detergent (use concentrate, and pour a little out so okay with expansion),and put in zip lock baggy.
I use my worst suitcase, in case it explodes, so I don't care if it get's destroyed (but hasn't happened yet in 5 times).
Finally, I weigh it so it's 45 pounds, and start another suitcase if needed. Then I use the cases for purchases on the way back.
Really, stuff is packaged so well nowadays, it comes out just fine. Cookies, chips, etc... and buy plastic over glass, and you'll be fine.
Hope this helps, Goldi
If you don't want to do this, people have mentioned using gardengrocer successfully.