Dreedo, a quick way of making a game with your A600 would be to use Shoot Em Up Construction Kit, as long as it's a vertically-scrolling shooter you want to make. But it's really easy to learn and use, even if it's pretty basic, and some people have made some really fun games with it.
You could also try your luck with GRAC or GRAAL, but I'm not too sure about them running on a 1MB system. Backbone definitely needs at least an extra 2MB to run, but it does run nicely on my A600 (with 4MB all up). One option would be for you to set up UAE on your home computer and emulate Workbench and these game maker programs, put something together that way, then compile it and test it on the A600.
Don't forget to download the entries for last year's competition to see what other people made. Some of those games were made with easy game-maker programs rather than coded in a programming language.
Congratulations on getting the PCMCIA CF setup working!