A while back, I explained how to use the handy Outfits feature of your inventory to create a wardrobe of complete looks that are ready to put on with a single mouse click. (See "The Ins and Outs of Outfits.")
However, it's possible to run into difficulty with this feature, and a person asking a question on the SL Answers forum brought it to my attention (thanks, Chinook!)
Outfits are intended to be made up of LINKS, those useful items in your inventory that point back to an actual object, helping to keep your inventory organized. They aren't made for containing the actual objects themselves.
When you buy a new dress or shoes, DON'T store them in a folder in My Outfits! If you do, you could experience odd behaviors like your shoes being dumped into the Trash folder. Unpack the dress or shoes, and store them in your Clothing folder. Then wear them, and assemble the other parts and accessories you want for your complete look.
When you have it all together, use the procedure from the Outfits post to save it (Appearance--> Edit Outfit--> Save As.)
And glam on, Fashionista!