Lunch box sized, then drop what doesn't fit in it at my house
I'm pretty sure mine are 48 quart sized, one scraggly bull or cow that I shoot will fill them with room for ice, but I have been eyeing a few bigger coolers but am too darn cheap to throw that money down on the new cooler tech.
No problem getting a frozen boned out elk in a 150, the problem you might have is if it isn't frozen already, you won't have much room for much ice. Stop at the nearest location you can find dry ice and throw in a couple blocks. If you throw in a couple news papers on top of the meat and the dry ice on the papers you should be good to go.
I didn't debone fully, took a 100 and a 70 to hold a 6x6 and I think about 60# of ice. Cape etc. was wrapped up in a tarp and covered with a sleeping bag(and another 20# ice). This got me back to Wisconsin from Ten Sleep WY in very warm temps with no problem.
I am taking a Coleman 6 day 120 cooler out for my cow hunt,my son takes a 150 out for his bull. It took both to bring my moose home. Takes two people to handle them if they are full.I have used block ice and also dri ice.Either works but don't let the dri ice touch the meat.