Tell me more about doing this?
How do you secure the cooler so it doesn't open but still allows TSA to look in side?
Do you have a 'normal' cooler or something special?
I am imagining using a strap but thinking it would have to go through the handles so it stays on the cooler
We use an Igloo Wheelie Cool hardside, the kind with a drop-handle on one narrow end. The luggage strap is a heavy-duty with a snap buckle, and yes, it threads through the handles (including the pull-handle; which is held down by the strap when checked.) To make sure that TSA or airline staff don't have trouble hooking it back up properly after they open the strap, I duct-tape the strap to the cooler on the bottom and at the lower sides; that way they can open it up easily but not lose the strap.
Normally the way that I pack it is to put down a towel on the bottom, put in a large clear garbage bag and put the food inside the bag. All items are individually double-ziplocked and have some paper towels included if there is any liquid in the item that could leak.
If I transport things like frozen casseroles, I deep-freeze them in unbreakable cooking containers and pack them in as tightly as I can; they keep themselves frozen for a long time if there are no air pockets in the cooler (if frozen in a deep-freeze and packed in tight with insulation, these will normally not begin to thaw for about 12 hours.) Once everything is in, I push out the air, tie up the large bag, put another towel on top, then close the lid and strap it down. Notice that I do not put in water-ice -- it thaws too fast and leaks too easily, and airlines normally ban it in checked baggage. The added bonus of having everything in a liner bag is that once you arrive you can easily pull the contents out and be able to quickly fill your cooler with ice for drinks.
To lessen the hassle; I also print up a piece of paper that I laminate and tape securely to the lid, noting what is and is not in there. "Non-perishable dry foods. Contains no liquids, contains no Dry Ice, contains no glass." or "Contains frozen food items in sealed containers. Contains absorbent, contains no glass; no dry ice.." TSA will still look, but they normally won't have to totally tear it apart if they know what they are supposed to be seeing.
Dry ice is actually permitted, but the FAA considers it a hazardous substance; it requires use of special vented shipping containers. Much easier to just avoid using it at all.
PS: The Wheelie Cool is a 38 qt. model; it measures 23" x 13" x 16"; well under the 62" cumulative dimension limits for baggage. It weighs about 6 lbs empty, and I've never had it exceed 39 lbs. even when fully packed, because the towels take up space. It counts as "normal" checked baggage.
Also, I should note that if you do pack perishables, the airline will make you sign a waiver that you understand that the airline can dispose of the bag if necessary, without compensating you. If a long delay in a hot climate makes spoilage likely, they will get rid of the entire thing rather than take the risk it will ruin other baggage or draw vermin.