You guys appear to know a lot about this, so I have some questions for you.

I've looked into high-end ice chests, such as the Yeti brand, for car camping, etc. But their prices ranges up to several hundred dollars for something I would only use on infrequent longer campouts, and I already have several mass market brand coolers that are usually adequate for my needs.

Beyond the usual things like keeping them full, limiting opening frequency, and using block or dry ice, what might practically be done to extend their range?

I plan on getting some Reflectix insulation (basically bubblewrap faced with foil on both sides) for a different project. Would it be worthwhile making a cooler over-jacket out of that? Or is most of the loss incurred by air leakage and opening? If so, would it make more sense to add a gasket and maybe some means of clamping the lid down tighter?

Any ideas appreciated. Thanks for sharing your expertise!