I get a lot of files from one site that uses the a few passwords. It would be nice to be able to save them to a keychain and either have 7z test the password out on encrypted archives by maybe extracting one file to a temp folder or allow me to select the password instead of having to type it in over and over.
Password managers have similar functionality. Try using one of those together with 7-Zip. In the worst case, you will have to copy-paste the desired password.