Another friend of mine brought a bag full of these caps to craft night and I knew they would be perfect for this! I am pretty sure that they are the caps you find on the end of those long cardboard tubes used to protect posters and signs. They are the perfect size for us- nice and big and NOT a choking hazard! Very important around here with a toddler that never stops!
I tend to end up with unused letter stickers when I scrapbook, so I just used some old letters that I had in my scrap pile.