Best Offline Seller App

Hi there,
Can anyone recommend a good offline seller app? So many of the shops near me have very poor coverage and so I’m unable to scan products / check online when I’m in the store.

I have found one app that offers this but they only download the books database (and not other categories). I imagine it would be a pretty heavy download so ideally the app would allow you to select the categories you want / omit those that you don’t want to download!

Thanks!