We do a bit of a combo of these approaches - we keep a well-stocked pantry year-round (we host a cooking competition once a year, so it becomes more a matter of maintenance).

But because my wife and I both have pretty scheduled lives, we carve out time every Friday night (when we make lists of to-dos for the weekend) to divvy out meals for the week and determine what we'll make. Then we create a comprehensive shopping list for the week and do the shopping on Saturday. As I implied, it's not a matter of lack of availability as much as it is convenience to our lifestyles.

(As an aside, if Chinese and pizza are your only delivery options in PDX, you're missing lots of good choices - there are choices in every part of town and most of the 'burbs. Even where we live, between Beaverton and HIO...)