Hi Susan,
Thanks for visiting the Disney Parks Moms Panel. You likely will have no problems with any normal items that you would have in your purse or backpack. The main restricted items the security check is looking for are weapons, alcohol and glass.
You are welcome to bring in water bottles (as long as they aren't glass), non-alcoholic beverages, snacks, sunscreen and other personal items.
As for the recommended dress, Walt Disney World asks guests to use "discretion and common sense" to maintain the family-friendly environment. Attire that is considered inappropriate includes:
-- Adult costumes or clothing that can be viewed as representative of an actual Disney character
-- Masks
-- Clothing with objectionable material, including obscene language or graphics
-- Excessively torn clothing
-- Clothing which, by nature, exposes excessive portions of the skin that may be viewed as inappropriate for a family environment
-- Objectionable tattoos
I hope that helps. Please let me know if I can answer any other questions for you as you make your plans. Enjoy your visit to Walt Disney World!
Wilma