Are there any items which raise your maximum stats?

There is only one character that can raise its maximum stats: WX-78, the robot. It can eat Gears, which upgrades its maximum health, hunger, and sanity with each Gear consumed. It can consume a maximum of 15 gears, to get 400 health, 200 hunger, and 300 sanity. (The bonus is 20 health, ~6.66 hunger, and ~13.33 sanity per gear, rounded up.)

WX-78 needs this pretty badly, because it starts with below-normal stats.