You get 60g of wholemeal bread per HEXB so you'd have to weigh it but its usually about 2 slices of a small 400g loaf or one of an 800g loaf (so you can only have 4 slices as 2xHEXB's if you're on Red or Green and they're from a small loaf, you only get 1 HEXB on EE)
The cheese it depends what sort. Cheddar is 30g for a HEXA, or 45g of reduced fat cheddar. Different types of cheese are different amounts (and some you can have as a HEXB if you're doing Green)
Of course you can have anything you like on any plan if you syn it - 1 syn per 20 calories.