Here is my list from my past few trips when DH was 5 mos, 8 mos and 1 year, in no particular order....
Disposable Bibs
Regular Bibs for drool
Swim Diapers
Diapers
Wipes
Anti bacterial wipes/gel
Changing Pads
Shampoo/Body wash
Plane toys/room toys
Hats
Summer outfits
2 warm outfits
PJs
Socks
Bottles
Bottle bag
Zip locks for ice to keep bottles cool
Sunscreen
Bottle brush
Carrier of some kind or sling
Bathing suit
3 Receiving Blankets for shade on stroller and clothes pins to attach to the stroller
Crib Music Box/Bedtime buddies
Extra padding for pack n play
Attaching toys and rings for stroller
Toothbrush
Jacket/Sweatshirt
Variety of foods and snacks
Portable Hi-chair for hotel room
Swim tube
2 sippy cups
Travel garbage bags for stinky dipers
Disposable placemats
Common medications and thermometer (tylenol, cold meds, bug bite cream)
Carseat
Shoes
'Blankie'
Feeding bowls and spoons
Dish soap for washing bottles
Formula
Raincover for stroller and clips to attach to stroller
Stroller and stroller accesories....cup holders, extra bags that attach to stroller, rain cover
Very small diaper bag for the parks. I kept extra bag also with restocking items, but found it easier to grab and go with the small bag for a quick change, no digging around looking for things. It contained a diaper or 2, small pack of wipes, changing pad, small powder and rash cream.
I shipped many of the items I wasn't planning on returning with, i.e.; jarred baby food, baby cereals, plastic bowls disposable items, diapers etc...
Have fun!