There's a WRITE MEMBLOCK File Number, Memblock Number command. I the first 4 bytes stored are the size of the memblock, so you'd have to deal with that.
The other option is just to open a file and write all of the bytes from the memblock to the file:
fn=1
open to write fn,"myfile.bmp"
for n=1 to get memblock size(mem)
write byte fn,memblock byte(mem,n-1)
next n
If you use a single memblock to store multiple files at once, then use separators or headers between files or create a custom header that identifies the positions and length of each file type within the memblock. Then open the proper file and write the specific bytes to it.
If you are writing a memblock to a file, you only have to worry about writing bytes. You don't have to write dwords, floats or anything else. The bytes cover all the bases.
Enjoy your day.