Since you're asking about extras, I'll assume that you've got the traveling-with-little-kids basics covered: diapers, sippy cups, sunscreen, etc. Here are some things you might have missed:
- Gum. This is not sold at WDW or the Orlando airport. If you need gum to relieve ear pressure while flying, bring this from home.
- Stroller cover. Rain showers are common. Cover your stroller when you're on a ride, then you won't return to a wet seat.
- Evening in-room activities for the adults. My hubby and I have a travel Scrabble game and a deck of cards that entertain us in the room when the kids are asleep. A small reading light is a big help too.
- Cell phones and chargers. Good communication makes for a happier vacation.
- Water toys. We bring a small inflatable beach ball. Doubles your pool fun.
- Diversions for waiting in lines. Read more
HERE.
- Folding potty seat. Read more
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- Favorite snacks.
- Ziptop bags. For wet swimsuit, keeping souvenirs organized, saving meal leftovers, etc.
- Favorite blanket or other "lovey." Makes it easier to fall asleep in a new environment. A note of caution, you MUST put the lovey away during the day. Do NOT leave it on the bed. We once had a mousekeeper accidentally send a favorite toy to the Disney laundry with the bedsheets. We eventually got it back, but it was a stressful wait.
For more tips, go to the Moms Panel videos (in the box that currently says "Angela Bassett"). Disney Mom Heather has some great packing ideas shown there.
I hope you have a wonderful time making your first Disney memories with your family!