I'm a big fan of shipping a box ahead to the resort before leaving home. I saves me lots of money and packing space, too. I always try to pack things that will be used during the trip and not need to be shipped back home. Lots of snacks, foods, diapers, etc.... Be sure to make a list of what you shipped so that you don't duplicate. Also, ship it to yourself and put your arrival date on the package.
I buy & ship 8oz. water bottles and somtimes the 8oz pop cans, too. On our last trip, I spent over $15 in UPS shipping but I calculated that I saved over $40 from buying water & pop at WDW. If I can get a 12 pack of 8 oz water bottles for under $3, then I don't have to pay WDW over $3 for one bottle. Ditto with pop. This is a real saver if you are flying. If you are driving, though, you could easily pack them in your van.
When the kids were eating baby or toddler food (and in diapers, too), I would wrap the baby food jars in a diaper, then put 2 or 3 in a large ziploc bag for shipping. Nothing has ever broken in 3 years and I had the diapers & zipbags to use at WDW.
In case you need to ship something back, put packing tape, a label, markers, etc...., anything that you will need to ship it back. Just ask at the front desk where the nearest business desk is located. I know that BoardWalk has one. We just take the box there and they bill our room for the shipping charges. It is not cheap but it can be done. DH did that once with his golf clubs, too. They ship out of WDW usually on the next business day.
My youngest is now 5 yrs old but I still like to take the 8oz water bottles. Great size to freeze and take to the parks and a great size for kids. I give my DGD a frozen bottle on a bottle strap (that is looped onto the stroller to avoid getting lost) and she plays with it. The thawing bottles help to keep her a little cooler in the hot, summer sun, too.
One of the more bizarre things I have done is to ship a rocking lawn chair to WDW. Now, before you laugh at me, some of you parents will understand this. DGD needs to be calmed before going to sleep and rocking is the best way. I got a garage sale rocking chair and shipped it round-trip for under $20. (Yes, I shipped it back home when we were done.) It was the best money I ever spent on vacation! Much cheaper than renting a rocking chair for our 10 day vacation and we were able to maintain a solid nightime routine without ruining my back trying to "rock" in a regular chair.
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If you have kids that often need antibiotics, ask you doctor to write a prescription to be filled not reconstituted. Take it dry and mix it up if you need it on the trip. This will only work if you have a good working relationship with your doctor and they are in the routine of prescribing antibiotics over the phone. Your pharmacist can give you the low-down on how to reconstitute it.
GREAT THREAD!