This is a difficult one. When we plan trips, we usually plan well in advance. Plus, most bike thing are kept together - so, most is already packed.
As an example, the rain suits, cleaner, tire repair kit, compressor - all of that stuff stays in the bike. I aslo have a trunk bag that does on tops and specific items go in there.
Night before, we pack our clothes - have the kits already pack for biking. We pack for 3 days, regardless of how long we are traveling. Wife packs one less shirt because she "always" buys one. We stay in hotels and do laundry every 3rd day.