All excellent advice! Everything I would have said - especially marking the boxes with numbers and keeping an inventory list of the contents. Down the road you will want that one special item and won't know where it is....wahla....inventory list will take you right to the box it is in!
Tip on Storage Units:
Throw the contents of a box of moth balls on the floor of the unit. Will deter critters of all sorts. Can be easily swept up when you are done with the unit.