I usually make a folder on my hard drive for each trip. There I download by date all of my main camera photos (typically 95% of what I have to work with). I add a folder for any phone photos I might want to use. Another folder for my point and shoot waterproof camera. As I edit, I export photos from Lightroom all into a main folder of shots that are ready to use (Lightroom calls this file "Untitled Export by default). They stay in chronological order (mostly) because of the sequential numbers.
When I decide on a theme for a page, I move everything out of "Untitled Exports" into another file I label "holding file". From there, I sift through, choosing the ones I really want to use and have room for by moving rejected shots back where they came from (that "Untitled Export" file).
As other themes for pages start to emerge, I also make files for those to sort them for future use. I just did a book on our recent Sanibel trip and at one point had a generic "holding file", along with "general island shots", "pool shots", "beach shots", "Lighthouse shots" etc. As I do my pages and finish with those shots I move them back to that "Untitled Exports" file again. Now that I'm all done, I deleted the holding file and other miscellaneous files.
It's not really as complicated as it sounds!