I'd stay away from seafood. Beef gets "aged", old seafood just gets nasty. And corned beef, etc, are fine at room temperature for a few days. Salami, etc, for many days.
I move and send a lot of frozen meat (including fish) and some of my tricks are:
Freeze it REALLY hard. And not just the meat itself, but all the packaging. Whether in a styrofoam-lined box or wrapped in clothes in the middle of a duffle bag, the whole box/duffle is in my deep freeze (-15F) for days before I leave. Then, driving to the airport, the box/duffle is wrapped in a synthetic sleeping bag/quilt for the 4-hour drive. I know that helps, because the inside surface is quite cold to the touch when we get there, instead of having warmed.
Clothes are great insulation. If you are sending any clothes, wrap them around the frozen items. For 12-36 hours, that is ALL I do - wrap in clothes, a plastic bag, clothes, a plastic bag. Over 36 hours, I consider putting it in a styrofoam box.
For small quantities, talk to anyone at a medical office, hospital, or pharmacy. Vaccines, among other things, are shipping in 8" x 10" x 12" styrofoam boxes that holds about 2 liters inside. Cheap (free), lighter than ice chests (and therefore cheaper to mail). Pro-tip: There's not a lot of room inside to fit hard-frozen fillets, but if you put the unfrozen meat in, and fresh it inside the styrofoam box (leave the lid off), it will conform precisely to the interior of the styrofoam.
I never use water ice. If it is critical to keep cold, I use dry ice or frozen brine. Frozen brine (about 25% by weight NaCl) freezes/thaws around 10 to 15F. So all that frozen brine melts before any of your meat/fish/ice cream thaws. I've used this to transport ice cream to stupid places. It is also free, unlike dry ice. Well, almost free, maybe 25 cents for the salt. Use an old soda bottle, 90% full of brine and freeze that. Throw it away later or bring it home and refreeze it. It's DIY "blue ice" except it thaws at 15F instead of 32F. And also better than sending yourself frozen water (you can get water anywhere), is to freeze something containing water. Decant beer / wine / champagne into plastic pop bottles and freeze them. The beer and champagne will still be carbonated when thawed (I've done this many times). Then the beer/wine serves as your shipping ice but, hey!, now you have drinks with dinner!
Do this on group trips (rather than solo trips) because more is better. 4 pounds of meat has little more surface area than 1 pound, but represents 4 times the "cold" (more properly, it takes four times the heat gain to thaw). So it will stay frozen about 3 times as long. Using only clothes as insulation, one pound of hard-frozen meat wrapped in clothes is good for any same day travel. 3 pounds is good for 2 days.
On the trail, wrap things in your sleeping bag. That greatly increases the time it takes to thaw. Keep your pack in the shade when you can. Solar input makes a difference.
Using a few of these tricks, and you end up waiting for things to thaw. That is itself a trick. Check the temperature of the food in time to allow you to expose it to ambient temps in time for dinner. When I catered a wedding for 30 on top of Half Dome, I put a thermistor in the ice chest so I could check its thawing over two days (and found I needed to open it up and speed things along).