a couple days on the road and you will figger out where you like your stuff to be on your bike. everbody gots a different method.
consider a quick-release handlebar bag for stuff you don't want to leave on the bike for quick trips into the seventy-leaven, and for stuff you want quick access to while riding.....wallet, keys, cellphone, chapstick, sunscreen, passport, polaroid camera.
extra points if it has a clear sleeve or cover on top to hold your route sheets.
most bags leak. most rain covers do, too. tupperware!