I have a lot of the same advice, make sure the gear is insured, and you have documentation, pictures, serial numbers, etc.
As far as at the gig, I have a lot of the same advice there. I always lock my car doors, even if I’m only going to be a minute. I try to never separate my gear. If I do, it’s because I’m loading out, and we try to make sure there is a band member inside as well as outside watching the gear.
I don’t usually wander too far from the stage during breaks. I don’t really have a need to, so I’m always watching the equipment.
This is the important advice not yet mentioned. I don’t let friends of the band help bang gear, especially the friends that help just for the free beer. They may want to help, and they may want to be a part of the show, but they are not mindful, and more often just slow you down anyway. I’ve had people “helping” that the second we are done playing, they start lining stuff up on the sidewalk before we are even don packing things up, and then they don’t stay with the equipment to watch it. I have even had people “helping” that didn’t know which equipment was ours and what belonged to the other band, and then start loading the other bands gear into our truck. Then I just end up apologizing to the other band for the drunk accidental thieves we brought along. Not cool.
I have a system to setting up and packing up my gear. It only takes me 5 to 10 minutes, depending on how much room I have to move. Any help I get just slows me down and gets my gear misplaced. If you aren’t making enough money to warrant paying for a real road crew, then you don’t need it. Just my 2 cents.
Festival season can also be tricky, especially when you are in a tent. The back of the stage can actually be the unlit back edge of a tent. My bass player had a guy sneak under the tent and grab a bass off the back of the stage. Luckily a fan saw it and tackled the guy. Pay attention to your surroundings, I guess is the moral of that story.