just put him in a fish bag. If he's really big then a cheap styro cooler from the gas station will work. You could also use a 5g bucket, just put a lid on it to keep it from splashing in your ride. If you do the cooler/bucket method then the movement of the vehicle will keep the water aerated, in that short of a trip o2 shouldn't be an issue anyhow.
Either way, it'll be like buying a fish from a pet store, so no biggie. If he's really big (i.e. common pleco) then he shouldn't go into the 30g anyway, but that's another subject unto itself.