Oh... damn, that's actually pretty tough, but it's either Doctor Pepper, Irn Bru, J20 or Cream Soda.
Shame I don't get any of them very often. Cream Soda is sold by like two shops in a reasonable (15 Mile) Radius, the only shop within walking distance doesn't do it, and Doctor Pepper cannot be found anywhere in like 25 miles or further. Irn Bru's easy to get but I don't always have the Money for it, and J20 seems to only be done in Fancy Cafes and as 4 Packs that I can't carry on a Bike.
Such a Shame. =|