I have an overnight bag that’s always packed with everything. Two days clothes, swimsuit, all toiletries, eye glasses, chargers, cash, passport, etc. Only thing I add is my tablet and away I go for an overnight or two.
I have established checklists for larger trips. One for cruises and one for air travel. Sections for stuff to do a few days prior, like check the suitcase isn’t low on decongestant or toothpaste vs trip duration. Then stuff to do the day prior, like set out the clothes, with a complete inventory of what to bring based on trip duration, climate, and mission. Then a day prior section for relatively last minute things I can’t stow or do ahead of time. Like reload weekly pill dispensers, fresh beard trim, etc. And last of all a “Day of / Get out the door” checklist with everything from sunglasses to empty the dishwasher and take out the trash.
All of which works to almost eliminate last minute frenzy and “What did I forget?”. It also mostly eliminates not having something when you get there. Check each item off as you do it or put it into the suitcase(s), and when they’re all checked off, you know you’re ready.
It happens I’m leaving on a 2-week expedition type cruise on Friday. The checklist has 180 items on it. Many are inapplicable to an expedition but stem from the more typical drinking, dining, & sunning cruise, and there are also expedition-specific things added, like a wetsuit & hiking boots.
As of now, ~48 hours before departure I’m ahead of my usual pace and there’s about 10 things left for day prior = Thu and 15 last minute out the door things for Fri afternoon. All else is done and more importantly, known to be done.
That’s waaay overkill for someone who travels rarely. But if you’re gone a couple weeks a month like I am on at least one, if not two trips each month, doing it right every time gets easy. As long as you write down what you did rightly and add what you did wrongly to your checklist for next time.