Start by first making the goop.
The two things we use for this is corn starch(corn flour in UK) and water. I used two boxes and about 3 1/2 cups of water...but I would start by slowly adding water to the corn starch till you can roll it into a ball but when it sits in your hand it flows like a liquid.
Then add in some real flowers. We took these right form our garden. :)
A bin like this is great for sensory play. It covers 3 out of 5 senses
Smell~ this bin smelled amazing!
Touch~ All different textures, between the goop and different flowers
Sight~ Colorful, could add some food coloring too