How convert exe to zip file?

Does anyone know of any software or method to take a self-extracting exe file and (de)convert it to a zip file? I've just learned of a method to create a portable app for my thumb drive; but it presupposes a zip file as input. I have a number of paid-for applications that I would like to "portabalize", but they all came as downloaded exe's.

Thanks for any help provided,
Dick Y

Thanks to both of you for your helpful responses. It's an interesting situation. I already have Universal Extractor, and use it along with Winrar in my process to make portable apps (just started doing it yesterday, and have only made one so far.) The situation that came up, and led to my question is:
with some package exe's winrar will extract them, and I can then zip them for my process; (but Universal Extractor wont - that's why I wrote my question.)

with other packages, I discovered after Shawn's response, it's just the opposite.

So, I think my answer is to try UE first; and if that doesn't work, try Winrar. Yesterday I should have played around some more before giving up too soon and writing my question here.

Bottom-line, thank you both for helping.
Dick