If you do not have cinnamon chips or toffee bits, that's fine. Just use the oats, brown sugar, butter and throw in some cinnamon or pumpkin pie spice. Double it so you have enough to top the cake. You can use chopped banana chips for crunch or add white chocolate chips, what ever you want. Just get whatever crumble you make to be crumbly yet stick together a bit, so it crisps up nice.