We arrive at WDW always around 11 am. Luggage is usually stored for us at the resort. We ALWAYS pack a 'change of clothes bag'.
When we get to the resort we change from our Northern clothes to our
Southern clothes. The resort has never had a problem placing our
'change of clothes bag' with our luggage after we changed (in the bathrooms off the lobby). We keep our cell phone and call during the afternoon to see
if our room is ready.
2 suggestions - if you have a pass which willl allow you to go to a park the 1st day and you do not have small children wining to go to MK, go to EPCOT.
EPCOT never seems crowded mid-day.
If you can not go to a park the 1st day - pack swim suits in your 'change of clothes bag' and relax by the resort pool until your room is ready. Or go to DTD and walk around, take a boat ride, play mini golf, go to WL campgounds and visit the petting zoo.
If you do not have a cell phone or do not wish to use one, go to the information area of any park and ask to call your resort to see if your room is ready. Mind you - you should be staying at a WDW resort to do this from an information area at any WDW park.
I do not mean to be long winded. But experience helps to keep the familt calm and everyone happy. After getting very little sleep the night before we arrive at WDW can get my family a bit off-balance - but WDW magic always brightens the day