I quickly picked out 10 little items and put them into a bottle that was half filled with uncooked barley. You can use almost anything as the filler - rice (but I'm Chinese see, and it would really pain me to waste my staple food), any form of beans or seeds, even sand.
Initially I wanted to use sand, but that would mean either a trip to the beach or playground, plus then the bottle's contents would have to be washed. Too. Much. Hassle. We had some barley that was near expiration date so barley it was.
At first I thought I would print out the list of things for Poppy to find, and she could then tick them off one by one. But I didn't have the time to print it, so I just snapped a picture of all the items (yes, do that before you put them into the bottle), and showed her the picture on my phone.