I haven't read the full thread but here is my suggestions.
Collapsible Cooler is a must if you don't reserve a fridge at the values or if staying off-site at hotel that does not suppy a fridge. I use Ziplock bags for ice - less water mess when ice melts, just take the bag to the sink or tub and dump, then go refill with ice at machine. Always double bag the ziplocks inside the cooler. This will fit in your suitcase flat. I have tried the disposable Syrofoam cooler, I found it can be messy to use, as it will sweat alot and if move alot it will spring a leak. Always put a towel under any cooler to capture lost moisture. This way carpet or furniture does not get wet.
Packing liquids - especially if flying. Use Ziplock bags - double bag these also to protect against leaks. Snack size works well for travel size items.
Nightlight - put in bathroom area to help see at night, saves on stumped toes and you won't have to leave a light on.
Fabreeze to Go: works well as an air freshener and for fabrics in room.
Bring extra Zip lock bags with you of all sizes, you will need them I buy
Walmart's brand, best value in number of bags in box.
Always store items in day pack or bag in Ziplock bags, you will get wet in the parks, even the rides that give you a Dry area for items to store, (ie: Kali Rapids in AK) as you will find it will still get wet to some extent.
Bring towel or shammy with you to dry off seats that are wet after rain or on a water ride.
And did I mention Ziplock Bags?

Traveler's Best Friend. You can also store just about anything in them to help keep track of items in the room and at the parks. They come in all sizes from jumbo to snack sizes.
I also use a small 1 cup size Rubbermaid container for holding loose change and other small items.
A laundry bag or collapsible Laundry basket is good for keeping dirty clothes in one place.
Disposable Rain Coat is a must, buy in bulk at dollar store or walmart or you can create your own disposable Rain coats using Garbage bags, cut holes in for head & arms then fold and store in snack size Ziplock bags. Dispose of after rain.
Travel Bags do help in conserving suitcase space. I use one to pack my pillow, as I cannot use Hotel pillows due to allergies. I have also used them to condense my clothing down when space was an issue. Get the type that you squeeze the air out.
Power strip for power cords. Most hotel rooms are seriously lacking in electrical outlets for all things with power cords.