I-Spy bottles are a lot of fun to make!
I personally liked the colors and shape of the Walmart flavored water bottles so we used those.... after they were completely dried out, of course. You can google "i-spy bottles" and find a lot of great ideas. The i-spy items came from the Dollar Tree, Hobby Lobby and whatever I could find around the house.
Hayes loved separating everything out and making sure each bottle had just the right items. All three kids thought it was awesome to pour the rice in through the paper funnel. Like, totally awesome. Like, I swept up enough rice to feed half the neighborhood awesome.
It's important to not pour the rice (or birdseed) all the way to the top. You will want to leave enough space so everything can move around. Next comes the most important tip... superglue the lid shut.
I printed off simple labels showing the items to spy inside the bottle.