For instance: I've got my guns, ammo, cases, cleaning supplies, ammo containers, speed loaders, eye/ear protection... But what else do you consider a must-have item?
Spotting scope/binoculars, screwdriver/tool for adjusting sights. I also keep a 1st aid kit and a pack of quickclot in my range bag. Havent run across anything serious myself, but i know people who have and Id rather be safe than sorry.
I've got one of the $40 laser types from Wally World... It will get me on the paper every time, and it is nice to have. Definitely not essential in my book though.
I'd say Hoppe's #9 is essential. A close second would be ammunition
Now that I have one, I don't know I ever got by without one. You are never going to stop super thief. It should stop any kids and smash and grab types.
Training, its the best investment you can make. Cash is a good thing to have handy.
Don't forget armor. We spend a lot of money on things to send projectiles out, but overlook at stuff that stops them from coming in. bulletproofme.com is a good places for these things (prices are good too) if you want a whole setup. Or you can just buy a molle style plate carrier and get some level 4 rifle plates.