C.G.
You don't mention where you are going, but keep in mind that people in every country in the world have babies and you will be able to buy baby stuff wherever you go.
In fact, in Europe the baby food is 100 times better than in the US. We took an extended trip there this year and our son would scarf baby food down- here he wouldn't eat it at all.
Everywhere we have traveled with kids (east/west Europe, Asia) diapers have been very expensive so I would make sure to bring enough. The formula brands in other countries are different and they do not seem to have as many kinds so I would probably try to bring enough of my own.
As for everything else, unless you guve medicines like teething gel a lot I wouldn't worry about it. I did buy children's motrin in the Czech Republic and it was fine, but I would bring a thermometer so if your baby gets sick you can monitor a temp without trying to find a doctor.
I would recommned bringing some of those disposable bibs so you don't have to worry about washing bibs. Also, there are not many changing tables most places I have traveled so I carried a blanket with me to lay baby on to change and those scented diapers disposal bags in case I had to carry a stinky diaper with me.
You didn't ask but I will throw this in too;) If you are bringing a stroller consider a sling or baby bjorn type carrier instead. Most public transportation, monuments, and touristy places tend not to be very accesible to strollers and it will be a pain in the butt to lug it around. We rarely take a stroller anywhere becuase the kids tend to want to walk or be carried anyway. Also if you will be renting a car, make sure you have the clip for the seat belt that comes with the seat (usually clipped in on the bottom of the seat) in case the car you get does not have the LATCH system. Actually, all the rentals I have had did come with it but I would have to take chances.
Enjoy your trip and don't stress too much. If you need something you don't have it probably won't be too hard to find it.