Centennial is a pretty unique hop; difficult to substitute. A blend of Amarillo and Cascade might get you reasonably close.
CaraPils (not to be confused with Caramel Pils), also known as dextrin malt or the very closely related CaraFoam, adds unfermentable sugars (dextrins) to the beer that boost head retention and mouthfeel without contributing a lot of flavor. Usually about 8 oz per 5 gallons do the trick. It's also used in larger quantities for brewing very low-alcohol beers.