Many of them are infinite, so you'd have to provide them as functions rather than files. There's obvious ones like plain text, but some less obvious ones, like, PNGs are defined as a series of chunks, but there's no chunk count in the header, so you can keep appending chunks forever: https://www.libpng.org/pub/png/spec/1.2/PNG-Structure.html

This sort of thing is not just a funny question, it's something you think about when you're writing scanners. For instance, another "biggest possible file" is the zip file that decompresses to itself[1], which is in some sense also an infinite file. Many a scanner has been written that will fill the disk then crash if presented with that file, which is actually more pathological behavior than would be experienced if the scanner isn't there.

[1]: https://research.swtch.com/zip