In my experience - some of the sites that sell you stuff for this are expensive and they sell you a lot of stuff you don't need.

My suggestion - Look at the test and see what all you think you'll need to teach them.

You really just need the list of songs/pieces and a good playlist. I always made a playlist on YouTube and sent them the link.

It is impossible for you to have a competitive team if they do not practice outside of your 30 min a week or however long you meet.

They need to practice writing out the names of pieces and composers and know the spelling. Every letter counts.
(This is depending on what grade level they are in. Be sure to read the rules!)

There is usually about 2 pieces for each genre/style/or type of group. Classical - Jazz - choir - orchestra - etc

If you've got smart students who are committed you will be great. Most schools send very underprepared students to this event hoping to get some extra points because not everyone enters music memory students.

Hopefully you can meed more than 30 min a week.

But again - a lot of what they sell on those websites is a bunch of mumbo jumbo extra stuff. It's all actually really awesome lessons for teaching music but if you don't have a ton of time with these students it will go unused.

List of songs
Playlist
Set of rules
Motivated students

See if you can get on the list to grade these papers at the contest. It will help with your overall understanding of everything.

Good luck!