Firearms training class preparations

Here are some things I do before going to a firearms training class.  I just leave the small items in my range bag all the time.

- Verify functionality of the gun by shooting it for at least one session before the class.  In other words, don't come to a class with a gun that I've never shot before, since the gun might be messed up.
- If I haven't run this set of gear before, try it on all together. For example, I try on my holster, mag pouches, belt, and pants that I'm going to be using.  Even if you have experience running each individual piece, you need to make sure they all work together. You don't want to find out too late that your belt is too big for your belt loops on your pants, or the belt loops on your holster, or the belt loops on those particular pants are positioned poorly for the location that you want to run your holster or mag pouches.
- If I have adjustable sights, especially on a carbine, make sure they're zeroed before the class. Often the zeroing process on the first day of carbine class takes 2 hours or more, which is time that could have been spent learning. Bring the necessary tools to adjust the sights, even if they are already zeroed.
- Load all the magazines that I'm going to bring to full(check your local laws and make sure you're transporting them legally).  It saves a lot of time when the class starts if you're already loaded and ready to go. I've never seen an instructor that minded the student coming in with loaded mags, although it is possible you may have to unload one or two for some drill that the instructor wants to do. 
- Check that I have extra batteries for ear pro, optics, flashlights, etc.  Check that the batteries currently in those accessories are not dead.
- Label everything, including mags, loading tools, ear pro, even your holster and mag pouches if they are common.  I use a paint pen for this purpose.  Certain gear, I engrave with a cheap hand engraving tool. If you do enough training, eventually someone will grab your stuff if you leave it on a table or in a common area, not because they were trying to steal it, but just because they thought it was theirs. Having labels settles the matter if there is any dispute. I have had this happen to my mags, Uplula, and ear pro.  All mags are labeled with a number as well, to keep track of any mags that are malfunctioning.
- Check tightness on all screws/bolts, including any mounts on guns, lights, sidesaddle, optics, holster, mag pouches. I just kind of poke the screw with my finger in a turning motion, to save the effort of finding the appropriate bit for each screw, and to avoid breaking the Loctite if it was there.
- Pack an allen wrench set and a multitool which has needle nose pliers and flat head and philips screwdrivers just in case they come loose.  I just leave these in my range bag all the time. 
- Pack water and food if needed. Always more water than you think you need.  Sweets like candy and cookies are good for a burst of energy.
- Pack an extra holster if I have one.
- Pack lube and spare parts for the gun. Generally a recoil spring and an extractor will solve most problems on a semi auto.  For Glocks, a trigger spring would be good.  For ARs, a full bolt carrier group would solve the vast majority of problems. If shooting a carbine, always bring a cleaning rod, not so you can clean it, but so you can knock out a stuck case from the chamber. A magazine makes a good hammer for this.
- Duct tape and zip ties can be useful for field rigging a fix for holsters, slings, etc.
- Pack a baseball style cap, even if shooting indoors where sun isn't a concern.  This is mainly for keeping brass shells out of my face from the guy standing to my left.
- If it's going to be hot, don't wear a cotton shirt.  Once you get soaked in sweat, cotton gets very uncomfortable and takes a while to dry. If the temperature cools down as the sun drops, you can get cold very quickly.  Synthetic UnderArmor type shirts, or merino wool shirts are preferred.  Similarly, synthetic or wool socks are preferred over cotton socks.
- Consider bringing sunscreen and/or a shemagh or other neck scarf if it's going to be at an outdoor range. Sunburn is no fun and is distracting.
- Consider packing an extra gun if I have one, ideally the same caliber, and really ideally one that can use the same holster and mags. Note a G19 can use a G17's holster and mags, but not vice versa.  Depending on logistics it might not be worth it to pack a totally different gun with its own holster, mag pouches, mags, and ammo.
- Consider bringing a folding chair. Depending on the range and class size, there may or may not be sufficient seating.
- Consider bringing a bucket for brass. Most classes will let students keep brass that they pick up at the end of the class. People who reload or who think they might get into reloading would be silly to miss the chance to save some money and get free brass.
- Consider packing allergy medication or taking it in the morning if it's at an outdoor range.
- Depending on the range facilities, if running water isn't available, some wet wipes and/or hand sanitizer would be handy for wiping your hands prior to eating or after using the porta potty.  Don't underestimate the importance of this; I've gotten sick at least twice after shooting on ranges with no plumbing and using the portapotty without washing my hands.