The Spits frequently used a 90 imp gallon external tank, which is 409 litres.
Somebody posted, and I've reposted, a picture of the Typhoon carrying 4 rockets + drop tanks, and that's an option I'd like to see added.
The Mosquito pilot's manual also mentions a similar configuration, and warns not to fire the rockets for a minute after dropping the tanks.
The Mosquito's got a fair range anyway, but the Typhoon could really do with the ability to carry external fuel along with rockets.