My ideal nappy bag would be:
- light weight (some bags weigh a fair bit without stuff in them!)
- A single wide shoulder strap (suitable to go over the pram handles or across my body). Ideally adjustable in length
- 2 outside pockets, 2 inside pockets, and a large zippered pocket on the outside for adult things to be easily accessible like keys and mobile and wallet.
- have a sturdy base
- be quite large, maybe 50cm long by 20-25cm wide and 35cm tall.

Custom made nappy bags would be a great business for someone!