This trip preparation/packing/shopping list will prove useful on trips to Yellowstone, Grand Teton and most other parks!  Ideas were drawn from TA and other travelers.  Modify this list to meet your own needs.  A few items will be necessary if you go into Canada/Mexico.

Several of these items can be brought from home, while others can be purchased at full service superstores upon arrival at a base city.  If driving to YNP, much of this can be purchased and packed ahead of time.

Packing ideas: Organize your car with individual boxes, either cardboard or fixed or folding plastic.  One each for dry goods such as cereals, crackers, etc.; footwear/clothing; travel and field guides.  Bring (or buy locally) a large cooler, large because you will want to carry a lot of beverages and food while exploring.

Consider eating breakfast and lunch from the cooler; it not only saves money but gives you the flexibility to eat on the go which, at YNP, is a boon, as you won’t have to return to dining establishments at some distance from your location. There are plenty of picnic areas in the parks. Treat yourself to dinner at one of the park establishments, but don't expect gourmet meals.

Buy a cooler!  Carry beverages everywhere.

Home Preparations
Schedule someone to:
Check on your house regularly
Feed and play with your kitty /petsseveral times while you are gone
Mow the lawn/water plants
Check with local police department and request a “house check” while you are gone
Stop newspaperdelivery.
Stop mail delivery.
Pay bills so thatyou don’t have to worry about them while you are gone.
Leave a copy of your itinerary, insurance policy info, etc., with a family member
Heat turned down
Water heater turned down
Unplug appliances
Check in to the airlines on-line, print your boarding passes.
Packing and Clothing
You don't need a lot of clothes, especially not fancy clothes, but do bring comfortable layered clothing.  It can be hot during the day but quite cold at night.
Suitcases (amazing what you can get into a small one)
Laundry bag – good for carrying footwear as well.
Laundry soap (unscented)
Footwear: Sneakers, Sandals, Boots, Shoes (Unless hiking, sneakers and walking shoes are fine.  Don’t rely on sandals all the time, stones/dust, plus they can slip.)
Stormpants/jackets (e.g., nylon lightweights)
Sweater/light jacket for up on summits/ridges no matter how warm it feels at start.
Hats - A hat for sun and a hat for warmth. A hat which covers the neck and ears, as neck and ear sunburn at 6,000+ feet happens fast and feels pretty lousy.
Rain gear - yes, it might rain.
Glasses, sun
Glasses, reading
Nail clippers, tweezers and nail file
Lotions and Lip ointment- at high elevations the sun/dry air will parch your skin
Medicines, personal (get prescriptions filled inadvance of your trip)  PS If going to Canada, carry most current containers and/or current Rx.
First aid kit, including:  Band-Aids, anti-itch cream, Listerine/cotton balls (for bug bites), Tylenol, Ibuprofen, Tums, Neosporin, etc. and any other Rx you take. Cotton swabs.  Sunscreen/lip ointments.
Bug spray (Deet)
Pillows, for travel and extra sleeping pillows

Electronics and Notes
MP3 player
Notebooks (for travel notes and for the kids)

Important Papers and Documents
AAA/AARP cards
Golden Age Pass card (if applicable) or other National Park pass
Lodging reservation confirmations
Maps and related material
Resource books (among many, these are good):  Yellowstone Treasures, Geysers of Yellowstone
Passports, Licenses, Birth Certificates, Prescriptions (and pharmacy original bottles (if crossing into Canada )

Optics, Electronic, Computers
See this:
Binoculars – at least one good pair, 8 x 42, depending on number on trip; hard to share one with more than two folks
Spotting scope and tripod (see article, above – inquire of those with scopes rather than bringing one)
Cameras – consider point and shoots for the kids
Camera batteries, chargers, USB connector for computer, memory card(s), tripod
Computer to download photosand to keep daily journal
Cell phones and chargers

Basics for Your Car/RV and Lodging
Containers: Large and small, plastic type. Keep food and garbage in mouse-proof and scent proof containers. Includes the cooler.
Ice Scraper – It can get very cold at night
Ziploc bags –gallon, quart and sandwich size
Plastic trash bags –good also for laundry bags and storage
Garbage bags if camping
Compass and map.
Duct tape
Trekking poles
Camping chairs - folding
Matches/candle in asealed bag.
Flashlight/Headlamp: For the camper going to the outside head.  (And lest youexperience power failure or don't want to go bump in the night)
Games (Boggle, Scrabble, Cards)
Hand wipes and/or Purell for pit toilets -Purell is in restrooms but it might run out.  Typically, these are composting toilets, not rustic outhouses.
Note for hikers: Google “hiking clothes” for the wash and quick-dry models. They are thin and take up very little room.
Back problems?  Tie up a rolled foam mattress topper into your suitcase. Have one suitcase devoted to "equipment" such as the bulkier items listed above.

Paper Goods

Paper towels - use for napkins and cleanup

Toilet paper (You justnever know on a trip like this.)

Paper plates/bowls - or plastic reusable “camp”plates/bowls. Easy to clean, cheaper than paper plates, environmentally friendly

Tissues, e.g., Kleenex

Utensils and More
Forks, knives, spoons.  Store in Ziploc bag
Serving spoon, etc.
Sharp kitchen knife
Cutting board
Can opener
Cork screw
Coffee/Tea travel mugs
Water bottle, refillable, for carrying or a hydrationpack
Refillable water jugs to carry in the car

Shopping List, the Basics

Upon arrival at a “major” town, supercenters if possible for one-stop shopping.  Apply for a Safeway card if you use this store, some cost savings
Cooler! (A hard sidedcooler is worth the money, though Styrofoam works quite well; some might leak and they can be squeaky unless stowed carefully.)
Ice for cooler –block ice lasts much longer than chipped ice, though it takes up more room.
Cooler bag, soft sided - put the block ice in the bag and add the dairy products, deli meats, cheese, etc. Items stay colder and much longer when you store this bag insidethe cooler. It is easy to drain the melted ice
Bottled water for drinking.  The gallon is much cheaper than individual bottles and, refillable, environmentally appropriate.
Plastic refillable water bottles
Tablecloth – Thin vinyl tablecloth for picnic area.  Weighs little, folds small, wipes clean.  Clips to hold the table cloth in place - rocks work but not always easy to find
Tea, herbal or otherwise
Coffee, instant
Soft drinks
Coffee maker, coffee cups/mugs,(most lodges don’t have a coffee pot in the room)
Coffee/Tea bags,sugar, Splenda
Bottled tea/soda/water
Munchies: Pretzels, Nuts, Trail Mix (Gorp), Crackers, Energy and Protein bars, etc.  Granolabars (buy or make your own and pack them in the suitcase)
Bread/Wraps/Tortillas/Bagels (wraps takeup less room than a loaf of bread)
Cheese spread, cheeses, string cheese
Deli meats
Fresh fruit (don’tbuy too much, it's perishable)
Dried fruit
Veggies: avocadoes, tomatoes, cucumbers.
Dairy – milk, half and half, etc.
Yogurt, small multipacks
Peanut butter/ and jelly
Mayo, mustard,ketchup, sauces
Caviar, anchovy, canned tuna, chicken, etc. Keep left over storage in mind.

Powdered Gatorade, to keep salt in your system.

Mostly for hikers, two empty water bottles and some iodine tabs. One bottle for cleaning water to put in the camelback and one for mixing Gatorade (which NEVER goes in the camelback); always mark the Gatorade bottle so you don’t accidentally dump water in it that may have some powder left over into the camelback.

Field Guides: Geology, flora, fauna – Great resources amd books available at Yellowstone Institute, Audubon, National Geographic
Cooler - now what?  If you don’t want to ship it home, leave it for the benefit of the park employees, rangers,or other trippers.
Bear spray: Not usually needed for populated attractions or trails, but if you hike in the back country it's recommended by some. At the end of your trip, you can turn it in at the ranger stations or local police department of the town where lodged. UPS will not ship bear spray.

Have a wonderful time!