Most places offer a 'what to bring' list, I looked over the web site and didn't see one for them. I'd contact them and see if they have such a list.
A long sleeve button up shirt with a collar, and button it to the neck to keep brass out. It will be raining brass. HOT brass. You don't want it in your clothes with you.
I would carry two of the same gun if I could get another 19. I know, Glocks don't break, but Murphy loves ya. Especially in gun skool.
Ditto on a spare holster. And a spare magazine carrier, same as your primary.
You need more magazines, several more. You'll get some breaks off the line, that's when you load magazines so you don't miss class stuff trying to madly stuff magazines while something is going on you need to see/hear. You need enough magazines to be able to shoot during your periods of instruction on the line without running out of ammo in loaded magazines. Put your name on your magazines, you're probably going to have to abandon them on the line for a while when you do mag changes.
And you need a GOOD magazine loading tool. Otherwise your fingers are gonna bleed.
You need electronic hearing protection so you can easily hear range commands on the line.
Knee pads and elbow pads, if it's going to be an active class
A small notebook and a pen, to take notes
Bandaids - even with a good magazine loading tool, you're going to get blisters, cuts and dings on your fingers and you will need to patch them up. Don't worry about looking like a wuss, carry plenty of bandaids and you can give some to the tough guys who were too ashamed to bring their own. And fingernail clippers too. You're gonna break nails and get hangnails.
I usually bring the same "bucket seat" I use for dove hunting to gun skool classes - it's a good way to carry five or six gallons worth of misc stuff, and it gives me a place to sit down during breaks.
I bring lunch, the instructors I usually study with don't leave the range for lunch, and packing a lunch means having some time to chat with the instructors.
That's all I can think of right now, fwiw - enjoy yourself!
Mindset - Skillset - Toolset. In that order!
Attitude and skill will get you through times of no gear, better than gear will get you through times of no attitude and no skill.