20 qt yeti better , or a knock off to keep ice 5 days ?

Hey Rocky Top!

Any cooler can be much more efficient if used properly. Things like pre-chilling the cooler, using large ice blocks (rather than cubes), and keeping it in a controlled environment all help. For an extensive list, check out the recent article here How to Keep Ice From Melting - Buyer Benchmark

As far as specific coolers go, there are a ton of high end coolers that can achieve (realistically) over 5 days of ice retention. We all know Yeti, but there are quite a bit of coolers out there that are better performance wise and cheaper. If you want, this is a great review here to check out.

good luck!