**IT DOESN'T MATTER IF YOU MISS A CART! LIKE THE COLLECTIBLES, YOU CAN GO BACK TO ENTER THEM THROUGH CHAPTER SELECT, IN ANY ORDER**
There are FIVE CARTS in total full of ingredients, and you need to enter them all. The first one is more or less unmissable. The rest have to be sought out.
CART 1, chapter 7:
You'll come to a point where you are given a recipe for Luminosa, and have use it on the rats to unblock the path. The cart is behind where the rats were, in plain view.
CART 2, chapter 9:
You'll reach a point where you'll learn the recipe for Odoris, which lures rats. After using it on a person for the first time, luring a group of rats from a wooden bridge, cross over to an area with a soldier in front of you next to a lamp, and another soldier to the right hunched over a table. Ignore those soldiers and go left down the alley, turning left at the end and climbing over the stone wall. Use Luminosa on the penned in rats and proceed forwards to the cart.
CART 3, chapter 10:
After rescuing a story-related character, you'll eventually reach an outdoor area where you'll be taught Exstinguis, a concoction which puts out fires. Use it on the fire near the guard to proceed, go down the stairs and turn right, staying low beneath the hedgerow. Use Exstinguis on the soldier's torch, Odoris to lure rats to him if necessary, then follow around sticking by the right hand wall. Climb over the wooden fence, and turn right to climb another one, instead of heading towards the burning doorway. Use more Luminosa on the rats beyond to reach the cart.
CART 4, chapter 12:
In the rat infested garden immediately before the section where you defend the mobile firepit, turn left to see the Alchemist Cart. Use Ignis to light the lamp next to the cart, then Luminosa to clear a path to it.
CART 5, chapter 16:
Immediately after dealing with the first soldier in the chapter, proceed forwards and on the right will be two buildings painted with the white 'X' of the plague. The alley between these two buildings leads to another soldier, and the final cart.