On my 'Be sure to pack' list for ds (3) and I:
Small white noise machine (we generally sleep with white noise)
Ds's little blankie and his bear
A sippy sport bottle (found a Cars one) with a carry strap so it can hang off the stroller
Ponchos for all of us
Small cans of playdoh and other small toys for meals/waits
Large beach towel (placed in the bottom of the stroller basket, we can use it for sitting on, covering ds up to change him in the park, place over the sunshade for even more coverage on the odd chance that he might fall asleep)