I used to. Listed stuff for the box (hay/water/first aid etc), stuff for dressage, SJ, XC, niceties (sun cream, spare socks) etc etc etc.
After a couple of seasons I didn't need it any more, but always still take a moment to run through it in my mind and make sure I can actually put my hand on each item.
If you forget something there will always be someone to loan stuff. One event they put a call out for someone who had only brought their dressage bridle, and they wanted a 5 1/2 inch vulcanite pelham to borrow. The commentator put a call out for said item, and some minutes later had to plead for people to stop bringing 5 1/2 inch vulcanite pelhams to the secretary's - they had loads! One event a lady forgot her jacket, and the organisers moved her time so she could use mine once I had finished with it.
I used to keep all BE-specific kit like studs/bib/stopwatch/xc boots etc in a big lidded plastic box which I just took from tackroom to lorry & back again when we returned. At least then I only had to remember the bits and bobs that I used daily as the rest was taken care of
I have several large Boxes of kit that I take to every show, they are really sturdy but see through (Really Useful Box Co.) they stay packed on my shelves in the tackroom - 1 has 1st aid, emergency type stuff including stable Bandages, towels, basic washing, etc, 1 has spare kit so Bridle, girth, boots for each phase, 1 has misc show stuff, so studs, plaiting kit, number bib (medical card when it was needed) book shiner etc. I used to have a checklist for each box to make sure I'd put everything back.
My boot bag has my hat, hairnet, gloves spurs etc, I keep my everyday hat and boots in the car (tow vehicle) so push comes to shove I could use those.
The trick for me was to turn a long list into several shorter lists.
A last check is to visualise me and the horse in each phase and check I have each item we are wearing (including spare underwear - after falling off 1st horse of 2 in the water and having to ride 2nd with wet knickers)
If we need anything else it can be borrowed or even manage without it.