Depends on where you buy of course. In a supermarket expect a small bottle of beer to be around 30-40 baht, depending on brand. In a night bar usually 80-100 baht. In a 5 star hotel 130-160 baht.
Food can be as cheap as you want to get by buying from street side vendors. In a small Thai restaurant expect a thai dish to be around 40-60 baht per plate, or western food 100-120 baht per plate.