I have a master checklist of all the items I need and then I make up a photo chart of the clothes I'm planning on taking. That way I can see if the items all go together and can be used in several ways.

I stick with basic black pants and knit shirts (I'm a big fan of Duluth Trading Co.'s longtail shirts), and then add several colored jackets and big shirts. I really like the microfiber big shirts from Travelsmith. For cruise formal nights, I add a fancy silk jacket that will go with those basic black pants and tank top and add a pair of dressy sandals.

We're doing three weeks in Europe this fall, followed by a 15 day transatlantic cruise, which makes it a little harder because we need slightly dressier clothes on the cruise than on land. Still, I'll get it all into one carryon size bag and my Baggallini backpack purse.

Passport, tickets, money/credit cards, prescriptions

Things I've forgotten
jacket (!) Left on the sofa
underwear (!)
tops other than what I was wearing.
chargers, SD cards
binoculars on a bird-watching trip

The binoculars were impossible to replace during the trip, but most other things can be bought.

I even was able to replace a pair of prescription glasses on a trip to Ecuador, in less than a day for $100...amazing. Still had my sunglasses.

Underwear - nah! who needs it?
Chargers - now that really is a problem! ��

Chargers are important, but can be replaced. The charger for my cell phone died on my last trip and I was able to buy a new one ( after the national holiday was over...). Of course, it had a European plug, so I also had to buy a new adapter so I could use it in the UK and US. Sigh. I bought it in Budapest. This trip I bought a hair dryer in Berlin, thinking I could use the same (brick-like) adapter. No such luck.