First: start a new game on enchanted (I think, my English is bad so I probably wrote wrong), because have many many more resources.
Explore every building everyday.
At Wednesday, DON'T GO TO THE CEMETERY !.
go to every building to find the catnip, if you find all possible until Wednesday, you will have around 8 or 9 can (I think it's 9) at the start of Wednesday.
(enchanted mod will give you a can of catnip on Tuesday if I'm not wrong).
Edit: "health" pipe is so easy to find, when I did the achievement, I had 16 at the time