Just be a man and do the loop-fu manually
OR
Bug someone to write it for you!

(yeah, I am being super helpful)

yeah, that was the kind of thing I was thinking, but if this was taken to quite a high level some songs might become a lot less human readable; and it would be nice to have some code to do this automagically.

You can set loop points inside a pattern and save a ton of space. This is true of MODs too.

I use SHRINKXM (dos tool) for this. (google it) It doesn't make the patterns smaller but removes excess, trims sample loops and so on.   Because XM patterns are compressed (though not in a particularly optimal way) you can do some fixes yourself.   For example if you don't need to store the instrument number against each note then take it out, same with FX that only need the command rather than parameters.  You can usually clear a few bytes per pattern that way. The compression is described in a couple of docs , which should help you out with this.

The other alternative is to use compressed samples such as MO3 files (XMs with mp3 samples) but only some players can use them.

I've seen long-play one pattern songs with very slow BPM, with multiple replays of some passages (i forgot that command, sorry).
Probably from Jeroen Tel (WAVE/Five Musicians), check his small-size tracks in scene.org module archive.

Remember to delete unused instruments too. Those take up quite a few extra bytes.

Thanks for all the helpful replies, boobiesqueezer managed to shave off an extra 500 bytes

The samples in the song I'm working on should weigh in at less than 1k and the 5 pattern song is 21k.  It's got some fairly intricate programming, but that still seems big.

Got a few big projects coming to a close, so might take a look at the weirdo .xm restructuring idea over the holidays.

There's an optimize button on the main panel.

Pattern data should be fairly small for modules, not sure about xm, but I expect it's fairly similar.
How big are all the samples you use in a song combined, versus the XM for the same song?
You can load your XM into fasttracker and save them from there, just to make sure MilkyTracker doesn't save a bunch of metadata on it's own.

edit:
OK I guess it makes perfect sense for 1kb compos

Try BoobieSqueezer for reducing XM size. Though BoobieSqueezer works more in the instrument side of size cutting, though.

As for the miniature loop points... It's possible, but I'm afraid that has to be done manually. Sorry...

Writing chiptunes in milkytracker I can't help but feel the modules are unnecessarily large because of pattern data,

Surely it shouldn't be too hard to work out an algorithm to set hundreds of tiny loop points, making 3/4 of most songs redundant (if a bit human unfriendly).

is there something like this out there ?

did there used to be a "pack" button somewhere on soundtracker , or am I imagining that...