head bolts are reusable, so are exhaust and inlet gasket, unless they got holes in them
you could check for warped head with a ruler but i got told by head skimming guys that these differences are so small that they usually cant be seen by naked eye and will only show when head is on skimming machine
i wouldnt change timing belt, water pump, aux belt unless belts are cracked or in rly rly bad condition, but still i would personally just wait till it snaps, cuz even if it does it wont do anything bad apart from leaving your car on the side of the road