I travel a lot, probably once a month even if it's just for a long weekend. My "bathroom bag" is constantly packed (replenish at the end of each trip as needed) so it's really a grab-n-go. Toothbrush, tooth paste, shampoo/conditioner, deodorant, body wash, skin cream, face cream, floss, mini-loofah, hair brush, shower cap... all kinds of stuff is always packed. I have a "meds bag," my "nail kit," and "spare charger bag" also always packed, so with the 3 of these and my credit card, I can travel at a moment's notice! Then I have a "disney bag" that has stuff we only use at Disney- so ponchos, water shoes, hand-held fans, ears, plastic clips, small LED flashlight, stuff like that.
Regarding clothes and extras? I watch the weather and pre-plan, at least in my brain, and have a scratch pad for "don't forget" items, as well as a small box to drop these items into as I think of them, if possible. I sort-down my wallet a couple of days in advance, so I'm not carrying extra credit cards or other cards that I won't need while on vacation. I will start laying out clothes a couple of days in advance, and then pack everything the night before travel (except day-of essentials, like makeup, curling iron, nook, laptop). Really can't do it day-of, as the airport is a 2+ hour drive, plus have to be there 2 hours in advance; even a late-afternoon flight means leaving the house around noon, so packing in the morning would just be too stressful!