We just went in May with DS2, and here are some of the things I packed and sent ahead: antibacterial wipes, regular wipes, diapers, snack foods (applesauce cups, dried fruit, mini cereal boxes, snack bags of pretzels, etc), toiletries (I did carry on a couple of small toiletries in case we got stuck somewhere on the way down), dollar store ponchos, juice bottles, small toys/bubbles, extra paper plates/bowls, plastic silverware, a paring knife to cut fresh fruit, dish soap, disposable bibs, swim diapers, etc. Basically anything that wouldn't melt in the FL heat and would fit in the box (especially the heavier stuff so we wouldn't have to lug it into the airport).
We used UPS and shipped a 51 lb computer box for around $31
. We dropped it off on a Sunday (knowing it wouldn't go out till Mon/Tues-but DH had to carry the heavy bugger!) and tracked it's delivery. It got there by Thursday morning, and we didn't leave until Sat, so I knew all that stuff was there, safe and sound (and I knew who signed for it at OKW).
I called the front desk at OKW and asked them how I should address the box, to make sure it got there OK. I just plastered our address on each side of the box (leaving room to write our return address on each side also).
We did use the same box to ship stuff home (souviniers, leftover diapers/wipes/toiletries, dirty laundry). DH took it to the front desk on checkout day and they weighed it/sent it from there. We did make sure to take clear packing tape along to seal the box and a thick permanent marker to write our return address on the box.
Let me know if there are any other questions I can help you with.