Litter Picker Achievement in Little Kitty, Big City

This is cumulative, and the game doesn't even tell you about the existence of recycling items. Basically, all those random cans you find around the city can be recycled by picking them up and taking them to a blue recycling bin, which are very common especially near vending machines. Near the recycling bin, you'll get a prompt to press  to deposit the can in the bin. Doing so counts towards this achievement and also rewards you with a Shiny.

You assuredly won't do this naturally, but thankfully there is a fast and easy way to grind it out, which I have elaborated on in Fat Cat (25G). Refer to that solution for more information.