The pic idea is very helpful!
Agreed. Maybe one of the best ‘tips’ I’ve seen in a long time. But, even then, I’d still have concerns of whether I actually “put it in the bag” or maybe somehow left it just sitting there.
Ahhh, the joy of obsessiveness. Such a great sport/hobby for us obsessive types. Sometimes, I think that’s why some of us are drawn to it. Where being obsessive is almost totally normal.
I feel you. So in addition to the photo you can also also have a checklist and cross the item off the list as you put it in the bag. Then, take the checklist with you to gear drop off and when you dump everything out to make sure everything is still in there, you can use a different color pen when you recheck and close the bag and walk away. Sleep tight. 
Have a great race.
Might as well have a picture of the list as well, uploaded to the cloud and a Go Phone in your bike special needs bag, so that at mile 60…when you’ve had plenty of time to start thinking about stuff again, you can check and make sure that you indeed put your run belt and race bib in your T2 bag. Or at least, marked it on your list that you put it in your bag.
I do think that there is something to the fact that one of the draws of triathlon for a guy like me who is prone to mild obsessiveness, is that I can let my obsessive flag fly. I feel I’m almost justified in overanalyzing and overthinking and quadruple checking and trying to think through the what ifs to the level of “What if, the temperature somehow drops to 28 degrees on August 14th in the Midwest? I better bring that jacket and the spare kitchen sink…in case my primary kitchen sink craps out during the run.” I can get it out of my system in a mildly justified way. I sometimes wonder if it keeps me from letting this part of my nature invade my real life in a potentially disruptive way.
I mean, triathlon. It’s totally OK to do this. As long as it doesn’t hinder your enjoyment or your fellow racers. I also love in triathlon that you can rub slippery slidey stuff all over your slippery slidey bits in front of 800 strangers and nobody bats an eye, other than maybe somebody asking to borrow some.