It is 23:30, you are leaving for a full week on the field the next morning and you just started packing. It is impossible to keep the focus and you know you will forget half of the things you need…
We have been there and we know how it is.
You can make a list beforehand to make things easier when it is time to pack. Start the list a long time before leaving. That way you can think clearly without stress. An ideal packing list is dynamic (I use a spreadsheet). You can sort items by actions (sleeping, hiking, sampling, reading loggers, …) or by location (car, main bag, day bag, …). When on the field, or on the way back, list what you missed and what was useless. You can then correct your list, and after a couple of field trips you will have a pretty good packing list.