As a fun side-project, I created pico-build. With it, you can build multiple lua files into a single PICO-8 cart. Here's a demo gif showing the usage:

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There are a bunch of other great tools that do similar things. You should check them out too: p8, picotool, picobu.

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The main things that pico-build does differently from the other tools that I've seen are:

• Formats the separate lua files as tabs within the PICO-8 editor
• Launch/reload cart in PICO-8 and log printh() output in the terminal

I'm using it now for my own projects. If you try it out, let me know how it goes!

Nice, but cant you just #include all the code together?

Honestly if #include was available when I started working on this, I probably would not have made it because it covers most use cases. This approach has a few advantages though:

• Your code gets built into the p8 file as separate tabs, so your final cart will have the code organized instead of all concatenated into one long chunk.
• Auto-reloading the cart in PICO-8 is really nice for rapidly tweaking things.