Yes, keep a pad and pen handy and write down things you are missing, as people said above. I use a notepad on my phone, and write down any notes as they come up. What went well, what went wrong, what you need, and what you run out of or run low. I end up writing down something after each trip. Each time I'm in any store, I consult my phone to see if I can purchase anything here for the next trip.
Also, I have a checklist in an Excel spreadsheet of EVERYTHING. What's in each drawer, cupboard, compartment, etc. A week before my next trip, I check everything against this checklist. If I've done everything correctly, nothing will be missing, and items that I wrote down before were already in my checklist and purchased.
I also have a page on my checklist for each meal that I plan for my weekend. Not just ingredients, but special utensils, or other equipment that I might not normally keep in the trailer. Example, my "Lunch - hamburgers" page will include the ingredients, but also the grill, charcoal, etc. Each time I decide to add a new meal to a trip, I make a new page for it, so if I decide to make it again, I have a checklist for it.
The day I leave, I run through my checklist one last time, just to make sure.
Maybe this is overkill, but I know I have a bad memory, and this is what works for me.. Haven't had a major OOPS moment due to packing since I started this.
Let me know if you want a copy of my spreadsheet as a reference.