In your sentence it means a big pack of banknotes. It's too dangerous to stroll around with these noticeable things in the big cities.

Hello Safaa, Here in this context it is slang and means 'a large amount'.

It means a wad of money[ notes] because you may get robbed and your money will get stolen.

A variation of this is to "shoot your wad". This means to spend all your money in a short period of time - usually spending it on something useless. It can also refer to exhausting all your energy or resources.

Hi Safaa, If you held a bunch of tissues in your hand, soaked them in water then squeezed them so they stuck together in a ball, that's called a wad. You can also say 'wad of clothing', as long as it's squeezed up and stuck together. In this context, a roll of banknotes is nicknamed a wad, to give the image of all the notes stuck (wadded) together. Which also implies a large amount of notes.