J.H.
Hi K.,
I try to take 2.5-3 days worth. That way, I have enough to wash every other day (the 2 days worth plus some for the kiddo to wear while I'm doing the wash--thus more than just 2 days worth). If you're up for washing every day, you could cut that down to 1.5-2 days worth. However often you decide to wash the dipes while you're away, do be sure to budget some diapers to tide you over while you're washing the others.
And yes, I definitely try to run a diaper load as close to my departure as possible. That way, you can avoid having to travel with many stinky diapers or leave too many waiting in your diaper pail at home during your whole trip. Whatever ones I have to leave dirty at home I hang up (along the edges of the diaper pail, or in the shower--whatever works for you). If they dry and air out during your trip, they'll be less stinky by the time you get back than if you leave them in the pail, wet. It can't hurt to crack a window, too, to air out the room they're hanging in.
Good luck, and have a great trip!
Juliet