> For example, one format I use is just to concatenate multiple files into a single one, I use it to group video timeline seeker images into one file - it is faster than using archive or tar/gzip

I did something like this when I was moving my files onto a new computer like 25 years ago, and all I had was a floppy drive. Just continuously dump the data onto a floppy until space runs out and ask for another one until there are no more files.