For Montage classic you'll need to have your user bank saved to an X8U file.  If you have libraries you'll need those X8L files too.  Montage classic doesn't support the MODX backup files (X8A).

For Montage M, it does support loading X8A files so go ahead and have your complete backup ready in case you run into an M.

The other thing you could do is find a Montage at a store (friend, studio, next backline encounter) and load up all of your content using user and library files then save a backup with that Montage classic so you have an X7A file.  Then next Montage classic you encounter it's a one and done operation.

Be sure to TEST everything you transfer before relying on it.

How do transfer my modx8 user files and patterns and arpeggios to a Montage 8+... and retain functions as I am traveling and the venues only has Montages not Modx

Try not to assume that just because it appears to load ok on a different machine that it will actually play the same.

One safeguard is to plan time for a personal 'sound check' where you do a quick run through of key areas of each performance you rely on to make sure it behaves the way you expect. You don't need to play then entire songs just the parts that will trip you up, or be noticed, if something is wrong.

Another tip is to get in the habit of taking detailed notes on each machine you plan to use. Some of the older machines will still have older OS versions. Do a quick check of the utility area to find out, and write down, the OS version and note any libraries that may be installed.

Something that can trip you up out of nowhere is the fact that an instrument might have multiple performance with EXACTLY the same name. Then if you just search for a performance with that name and load it you may not get the one you expected. One way that happens is when a user names their performance with the same name as a preset.

So loading a USER file that replaces the user contents of the machine you plan to use is safer and preparing/using Live Sets, rather than category search, can also help prevent problems.

Some venues may not want you to overwrite their instruments user area so plan how to deal with that. I like to make sure I have time to backup the machine I plan to use before I load my user file and then, after the performance, restore the backup for them.