Listen to your kids when you are at the store and they are yelling "I want that." 

I have always sold kids clothes and items around the house that we no longer need, but one Holiday season my daughter wanted the new baby Bratz dolls.  I couldn't find them anywhere.  I finally did find some at a local store and I bought all that I found.  I thought if my daughter wants them and we can't find them, other people are probably trying to find them also.  I thought if I was wrong I could always return them.  I came home and looked on ebay to see what was listed, I then did an advanced search and only looked at closed auctions to see the final value.  I was surprised!  I put up the dolls I bought and I tripled the amount that I had paid for them.  The extra money came in handy before Christmas. 

Last year my daughter liked the Littlest Pet Shop animals, and again, they were hard to find in the stores.  So I check many of my local stores after their stocking days and buy all that I can get.  You do have to watch, because with this item there were only certain ones that were popular on ebay.

She did this with Tamagotchi toys and my son with Star Wars figures.  The point of this guide is to listen to your kids.  They have instincts as to what is popular and they want it - as do many other kids!  Items like this are nice because you sell them in the package and if they don't sell, you can always return them if you keep your reciept. 

Another tip is to make sure you list them for at least 20% more than you paid for them to cover your auction fees on top of the cost of the item.