As someone said, it would be good to add more money-types to one currency.
So what about when one currency will be fruit, then for example, 1 Fruit = apple, 2 Fruit = pear, 10 Fruit = cherry etc.
Or just totally random items having the same value.
And an extraordinary currency: Lightbulbs! (normal, neon, economy etc.), they could be in the streetlights, so the Knytt/Ball
could take (steal
) them.
Or some Liquids! The Knytt/Ball must find some bowl/cup to take the liquid from its place (lake etc.), then Knytt could leave it behind or keep it, so she won't have to seek it anymore. It could be collected from waterfall, rain or drops too.
Or repeat some Knytt items as currencies! (dunno if mentioned yet)
Or it could be powder from plants/mushrooms, Knytt will need some sack to take it, then she comes to that plant/flower/mushroom and she shakes it and the sack fills.