兜儿 is colloquial northern Chinese for pocket. Standard Mandarin uses 口袋 (kǒudài). 兜 can also mean 'to go around' as a verb: 兜风 (to go for a drive/ride).
memory
兜 looks like it has a 儿 (child) at the bottom — imagine a child hiding things in their pocket (兜儿).
